I was under the impression that an anti-theist was someone who actively pushed people away from deity beliefs and would make arguments about why gods aren't real while atheists were people who just decided not to believe in a supreme being.

Though, definitions are funny sometimes. "Pagan" originally meant "of the countryside/villager" and it morphed into "someone who believe in multiple gods" just because Christianity took off in cities first and many village people were just isolated enough to keep their old traditions.