People with a bias will define words and concepts in ways that support their arguments. An Atheist will say that there is no replicable data to support the assertion that there is a god. A person who believes in a god will say that all of life and all of reality is replicable proof that there is a god. It's all semantics, really, and how one defines the words and concepts will be ultimately shaped by the beliefs they hold. Neither one can prove the other wrong, or themselves right.

Disbelief in yes is definitely a belief in no. Webster's definition of "disbelief"...


Main Entry: dis·be·lief
Pronunciation: \ˌdis-bə-ˈlēf\
Function: noun
Date: 1672

: the act of disbelieving : mental rejection of something as untrue

But as I said before, if someone acknowledges that they don't really know one way or another (disbelief in yes), they are an agnostic rather than an atheist.