This is pure semantic sophistry.
An atheist says: I do not believe in -god-.
Therefore: it is a denial of something which is defined as existing. By not believing in what believers believe.
Personally the definition of -free thinker- might be more appropriate. Nothing to deny for starters.
Freethinker. I like that term, but Good luck in getting people to stop using Atheist.
But I always get annoyed by having to justify the term Atheist to believers, so I don't!