The track is an anomaly in that it's one of the few that didn't unfold conceptually as it was written. "'Stan' was one of the few songs that I actually sat down and had everything mapped out for," Eminem told VH1 in 2002, "I knew what it was going to be about." The idea came after he was sent the beat by producer The 45 King, who heard Dido's "Thank You" on an advert for Sliding Doors, taped it off the TV and added beats and the bass line. "Her words instantly put me there," Eminem said, "'Your picture on my wall' – this is about an obsessed fan. That's all I kept thinking." source: https://www.vice.com/en/article/a3kj5j/eminem-stan-fandom-obsession-deep-dive

We can't really say for sure it wasn't intentional. Hopefully he has an interview in the future that clears it up. Just saying that there is a difference between the logical conclusion that he didn't intend it, and outright saying he didn't intend it. I don't think he intended it, but there is no proof that he didn't until he says so.