I don't recall most forums being particularly welcoming either or very good knowledge bases. Probably the main difference is the default for visibility of non-members, which does make a little bit of difference but I think if you want to maintain a knowledge base you should run a wiki, if you want a community then a forum or discord guild is the way to go, and discord is way easier for most people to set up.

The user is not saying that there was an evolution from forums to Discord, they are saying the popular digital space people go to has changed.