iirc didn't Wittgenstein take the view that it was better to understand how words were actually used rather than to be unduly picky about how they were defined.
On that basis it seems clear from all that has said than when atheists who are members of this forum use the term 'atheist' about themselves they mean that they don't hold a belief in Gods.
I can't see that it is, or needs to be, any more complicated that that.