A year, perhaps, after the first Ghostbusters came out, my brother got a children's book based on the movie, illustrated with stills from the film. It didn't have a story, but it was structured as a guide for somebody wanting to start a Ghostbusters franchise operator. It listed advanced equipment needed (proton packs, traps, storage facility) as well as more basic needs: advertising, a vehicle, a base of operations (ideally a derelict firehouse, but other abandoned buildings could also work).
It also had information about the Ghostbusters personnel (although just Peter, Ray, and Egon). As I remember it, the book (which included a fair number of references and jokes that would have gone over the heads of its elementary school readers) said that Peter was "trained" at Columbia University.
There is not a very rigorous canon for Ghostbusters material; there are lots of contradictions between the movies and subsidiary media. Even so, this picture book would probably be among the least canonical sources. Moreover, I cannot find any reference to it online (but that is more a matter of there being a lot of Ghostbusters children's books, and this one was apparently pretty low profile). However, I figured that it was worth posting what the book had said about the matter.