Depends on your definition of 'atheism.' If by atheism you refer to militant atheism, where the possibility that any sort of deity might exist is denied in principle, then you are correct. But that definition of atheism is a strawman lacking any utility, since few 'atheists' are actually that dogmatic and closed-minded.
If a self described "atheist" is not 100% certain that there is no God then, by definition, he is an agnostic.
Being a true atheist requires more blind faith than was shown by St. Thomas.
Sir, I have the right to define both what I believe, and the term to be used to describe that belief. Just as do you. I don't tell you what term to use to describe your belief, philosophy or religion, and I expect you to accord me the same courtesy.