It depends a great deal on your definition of the word cult
According to Websters dictionary
1 a religion regarded as unorthodox or spurious
Absolutely, the early Christians were seen (by the Jewish community) as a breakaway group following an unorthodox rabbi
then we look at another definition from Webster's dictionary
- a system of religious beliefs and ritual
Again this definition works. Christians had a system of religious beliefs and rituals that set them apart from others in their time.
Then we have the Roman "Mystery cults"
https://www.metmuseum.org/toah/hd/myst/hd_myst.htm
Academics use the word cult more in the sense of Webster;s definition 1 & 3.
Walter Burkert has a book on Ancient Mystery Cults, Harvard University Press in Greece and Rome.
Judith Hadley writes about The Cult of Asherah in Ancient Israel and Judah: Evidence for a Hebrew Goddess
In popular culture the word cult is used differently.
Some people use it to mean Any religion different from mine.
Others use it to refer more specifically to small groups that try to control their followers like Jim Jones and the Peoples Temple, a new religious movement, between 1955 and 1978.