You best check up definition of atheism then.
Atheism is lack of active belief in gods, it says nothing whatsoever about knowledge/probability.
I am an atheist and even i acknowledge the possibility of god's existence, like i acknowledge possibility of existence of many other unseen things. Like giant caterpillar aliens, etc. I have to because any other position would imply i know every single creature in the universe.

PS: the position you described is agnostic atheist.