The categorical error is that none of it was a "come from", rather it was a "passing through". The sites were all popular waystations, but none of them owned the creativity of their users, they just happened to host the party, and once the party died down something new came up and the same users moved on to that thing. Thus the large number of Twitter users who will post things starting like "in my 4chan days" "in my SA days".
And other lies 4chan users tell themselves to feel important.
It wasn't even true back in the day, a lot of stuff came from SomethingAwful and Newgrounds... Then came Twitter!