@matrix
I think there could be some truth to it. Atheists are more likely to be leftists, but not necessarily because there's something inherently leftist about not believing in supernatural beings. It's more because of what is usually associated with the right wing.

Anti-abortion, bigotry against LGBT, climate change denialism, attempts to force religion into schools etc. An atheist sees all of those positions as being motivated by religion, and since he left religion, he'll go almost automatically to whatever is opposed to that.

And once he reaches his new tribe, an atheist might be compelled to adopt most other left wing positions on the basis that it opposes the right wing, that he now strongly associates with religion.

And that's why I think an atheist is more likely to be on the political left.