Premise 1: Having a God Concept makes any belief system a religion - if a belief system features a belief about God then it is a religious belief system
Premise 2: Atheists have a God Concept. They have a position on God, an opinion on God that qualifies as a position and an opinion on God, even though Atheists either see no valid reason to believe in God or explicitly reject such a belief. The point is, they still have God-beliefs
You cannot spell "Atheist" without the word "Theist"
The Atheist God Concept is that God is made up by humans who didn't know any better and is nothing more than myth
Conclusion: Atheism is a religion
Edit: I no longer believe Atheism is a religion. But I do maintain that it is a religious position, so is the same type of thing as religions