So you're suggesting that someone with no introduction whatsoever to religion, (assuming this were possible), and no personal idea about the possibility of the existence of god(s) would be an atheist?
If that's your point then I tend to differ. And the reason for that is all the claims I hear from Christians here who say, "I used to be an atheist", when all they really mean is that they didn't used to hold any real interest in religion one way or the other, then became interested in Christianity.
I don't see that as atheism. Unless I'm still misunderstanding you, you're claiming theism as a belief, and atheism as either a belief that god(s) don't exist or the lack of belief in gods. To me the lack of belief insinuates a lack of interest or never having been introduced to the concept. I don't think a lack of interest or ignorance of the concept qualifies one as an atheist. To be an atheist one has to be interested enough to explore the topic, and to discover, through that exploration, sufficient cause to hold the belief that no god(s) exist.
Not caring about the potential for the existence of god(s) isn't the same as atheism just like not caring about the evidence for or against evolution doesn't make one a creationist.
Theism and atheism are both beliefs. If you disagree, please explain.
If I'm still just missing your point, count this as one of my really off days.