You're right, it's not even remotely a religion. However, you can't just make an poll asking everyone's religious beliefs and leave Atheism out. I'm certain that's where the TC was going with including it instead of saying that Atheism is a religion.
If it was absent we'd all be complaining!
Anyway, the poll is currently at 115 Christians and 109 Atheists. If only it were more even like that IRL.
(EDIT: Don't know why I had "110". Guess I automatically round up in my mind for some reason)