I don’t even remember ever posting there.

That's not necessary for a ban. I'm banned in communities I didn't even know existed until I got the message I got banned in it lmao.

Lemmy is very similar to reddit in that regards. Mods apparently have zero shred of authority or respect IRL, so they abused the little power they have online to compensate. I'd argue that lemmy mods are even worse than reddit mods.