An atheist is someone who does not believe in Gods. It doesn't require the existence of a particular belief in order to not believe in it; in fact, not believing in something is the default position. You don't believe anything unless you are told something about it first, or find out about it on your own.
Do you believe in fadgdvaet? Probably not, seeing as I've just coined the term in the last few seconds. You don't believe in fadgdvaet now, and you didn't believe in him 10 minutes ago, or 10 years ago. So you've been longer without belief in fadgdvaet than I have with belief in fadgdvaet.
Do you believe in fadgdvaet? Probably not, seeing as I've just coined the term in the last few seconds. You don't believe in fadgdvaet now, and you didn't believe in him 10 minutes ago, or 10 years ago. So you've been longer without belief in fadgdvaet than I have with belief in fadgdvaet.