> I don’t remember all of the details, or if it ended up being true

Not as far as any link between the disappearance and D&D, no:

https://en.wikipedia.org/wiki/James_Dallas_Egbert_III#Disapp...

> and there was a Tom Hanks movie about it.

Mazes and Monsters, the novel and the movie, were inspired by the (false) story of the event.