Presumably because they all traveled there for a temporary part of their lives. And after university, they presumably scattered to the places where they built their careers and families.

"at university"

Clearly proximity is involved

Because for a lot of us it’s hard to imagine finding a half dozen or so people who can talk in person like that outside of a conference or workplace. Discord facilitates that because it assembles people based on interests and such. You’re just going to more easily have that kind of conversation than you would “out in the real world.”

My guess is they are functionally saying “this probably happened on discord if anybody is wondering how this is even possible and not made up for effect” but I might be interpreting too much