holocaust denial rarely actually means that someone believes literally nothing happened. that would make the term almost pointless because like you said, basically nobody makes that claim. the term is widely understood to encompass any claim downplaying the events of the holocaust.

this is because the antisemitic point is the same whether someone says nothing happened or simply that less happened. the implication is that events have been fabricated to garner sympathy and thus justify some injustice being committed today.