Provided that GMark was written before the Jewish-Roman war, and that the historical Jesus preached that the temple would be destroyed:
Without entering into debates about the character of the historical Jesus, it would not be unthinkable for a Jewish preacher/prophet with an apocalyptic orientation to preach that the temple would be destroyed again. And said preaching could even have helped the missionary work of early Christian communities after it indeed got destroyed, helping the "Jesus movement(s)" to persist while other messianic movements of the same period didn't. It may be surprising, but doesn't require supernal inspiration.
Besides, most scholars date the Gospel of Mark during the Jewish-Roman war, potentially after the temple's destruction (see quotes below)
Matthew and Luke used Mark, and were almost definitely written after 70 (see the New Oxford Annotated Bible introduction to the Gospels or this for quick reference), so the fact it is in all three doesn't add much to it being only in Mark.
big annex: quick quoting on dating & textual analysis
New Oxford Annotated Bible (intro section of Mark's Gospel):
Authorship, Date, and Historical Context
Mark was written anonymously. The designation “according to Mark” was added in the second century ce, as Gospels began to circulate beyond the audiences for whom they were written. One early second-century source claims that “Mark” was the apostle Peter’s “interpreter” at the end of Peter’s life, but no other evidence confirms that connection. Others have identified Mark as the “John Mark” who traveled with the apostle Paul (see Acts 12.12,25; 15.37–39; Col 4.10; 2 Tim 4.11; Philem 24), but none of these passages link John Mark with a written Gospel. Though the author’s identity is unknown, scholars find clues about its author in the Gospel itself. For example, its awkward style suggests that Greek was not the author’s first language. Other details, such as the imprecise citation of Jewish scripture (1.2), the over-generalized portrait of Jewish practice (7.3–4), and problematic geographical details (5.1,13) suggest that the evangelist was a Hellenized Jew who lived outside of Palestine.
The Gospel appears to address a mixed audience of Jews and Gentiles who faced persecution because of their devotion to Jesus of Nazareth as the long-awaited Jewish messiah. Early church tradition saw ties to the Christian community in Rome, where Nero punished Christians as scapegoats for the fire in 64 ce, which raged for nine days and devastated much of the city (see Tacitus, Annals 15.44). Most scholars today opt for a different context in the same time period. They argue that specific details in Mark 13.9–13 are better suited to a setting in Syria-Palestine, where Jesus’s followers may have been hated by both Jews and Gentiles for not taking sides, in the Jewish War (66–72 ce).
Notes:
13.1–37: Jesus predicts the Temple’s destruction and cataclysmic events to follow (Mt 24.1–44; Lk 21.5–33). Mark uses this teaching to interpret his audience’s present reality (see esp. 13.14).
14: Desolating sacrilege, allusion to the defilement of the Temple during the Maccabean Era (see Dan 7.27; 11.31; 12.11); may also refer to the Zealots’ occupation of the Temple during the Jewish War (66–70 CE). Let the reader understand, addresses Mark’s audience, perhaps to support those who fled the violence in Jerusalem.
Similarly, the HarperCollins study Bible:
THE TEXT DOES NOT PROVIDE clear evidence of the place of writing or of the audience. An old Latin preface to Mark states that it was written in the regions of Italy. Clement of Alexandria, according to Eusebius, wrote that Mark was written in Rome for the Christian community there (Ecclesiastical History 6.14.5–6). John Chrysostom says that Mark was written in Egypt (Homilies on Matthew 1.7). Some modern scholars conclude that Mark was written in Rome, citing the tradition about Mark’s relationship with Peter and the influence of Latin on Mark’s Greek as well as Christian tradition.
Others locate the composition in Palestine or Syria because of the many references to localities in Syro-Palestine and the interest in Jerusalem and the Jewish war. These scholars attribute the influence of Latin to Roman cultural presence in the region. The use of Aramaic terms and whole sentences, along with translations of these in Greek, suggests that the author was aware that some in his intended audience knew Aramaic and some did not. It is clear from ch. 13 that Mark was written during or soon after the first Jewish war with Rome, which began in 66 CE and reached its climax in the destruction of the temple in 70 CE. The occasion of the Gospel may well have been that war and the appearance of Jewish claimants to the role of Messiah. In that situation the author wished to reassert and interpret the claim of Jesus’ followers that he was and is the Messiah.
Notes:
13.1–37 Cf. Mt 24.1–44; Lk 21.5–33. Introduced by a prophecy of the temple’s destruction (vv. 1–4), Jesus’ speech about the end of the age (vv. 5–37) has some similarities with the “farewell addresses” of the patriarchs to their sons and of biblical leaders to their followers (see Gen 49.1–33; Deut 33.1–29; Josh 23.1–24.30; Tob 14.3–11; Jn 14.1–17.26; Acts 20.18–35).
13.2 Predictions of the earlier temple’s ruin were made by OT prophets (Jer 26.6, 18; Mic 3.12).
13.5–6 The many who will come are either people claiming to be Jesus or, more likely, those who claim to be the messiah of Israel and to exercise the power and authority that, from the point of view of Mark, only the risen Jesus has. Such military leaders with royal aspirations appeared during the Jewish war with Rome in the late 60s CE.
13.14 Mark implies that the prophecy of the desolating sacrilege in Dan 9.27;11.31; 12.11 is about to be fulfilled. The expected event is probably the setting up of a statue of the emperor in the temple, i.e., that after their victory in the war, the Romans would actually do what Caligula had attempted in 39–40 CE. Fleeing to the mountains recalls the flight of Lot and his family from Sodom in Gen 19.17 (cf. Rev 11.8).
(note that the argument here is about the framing of Mark 13, not the mere statement that the temple will be destroyed)
Jewish Annotated New Testament (last one, I swear!):
The shortest of the Gospels, Mark was likely one of the sources for Matthew and Luke; the Gospel of John may reflect an indirect knowledge of Mark, but is also possibly independent (see Introduction to John’s Gospel, p. 67). Although good literary reasons support this source-critical view of Marcan priority, it has religious implications: the claim that Mark’s Gospel is the earliest Gospel, a claim that developed in the nineteenth and early twentieth century especially in Germany, made it easier to downplay the Jewish practices of Jesus which are more prominent in Matthew.
The Gospel of Mark was likely written between 64 and 72 CE, the time of the First Jewish Revolt against Rome when the Jerusalem Temple was destroyed, several decades after Jesus was crucified. References to the Temple’s destruction (13.2) and to wars (13.7) as well as the depiction of refugees (13.14–17) could apply to the events of that period, although they are too general to secure a precise date. Cogent arguments have been made for the Gospel’s origins in Rome, where Papias places Mark, but also for southern Galilee, northern Galilee, or Antioch in southern Syria (see map, p. 70).
The evangelist (henceforth, Mark) probably utilized a number of sources for the Gospel including a Passion tradition (that is, the account of the days leading up to the crucifixion of Jesus), stories of healings, accounts of conflict with Pharisees, and parables. Mark’s Gospel also reflects a rich use of the Septuagint (LXX). A few texts—Daniel, Isaiah, Deuteronomy, Zechariah, and some of the Psalms—are quoted often. But while Mark quotes Jewish Scriptures often and generally places Jesus’ and John the Baptist’s preaching within the range of Jewish religious concepts, Mark expresses ambivalence or even antagonism to the Jerusalem Temple (see 11.12–25nn.) as did other groups within Judaism, such as those associated with the Dead Sea Scrolls.