They were incorrect. I've never seen any confusion on his origin.

It's possible that those memes were about attempts to map the fellowship to DnD classes, which is (1) something lots of people have tried to do (2) an exercise in futility, because only some bits of DnD have ever been based on LotR. Gandalf is too skilled at fighting to be a typical dnd wizard, and his magic is mostly limited by the rules he was given when sent to middle earth, so we don't see him casting spells the way a game wizard would.