The Sects of Atheism

[Angrboda]

I think it mostly has to do with confusing things common to being contemporary westerners for being common to atheists - like not believing in the supernatural..which is a common belief even for western god botherers.  The arc of western culture over the past few centuries has been the rejection of superstitions (whether we're actually doing a good job of that..well..jury's out).

It probably also has to do with some confusion between the characterizations of atheism as lack of belief and of atheism as rejection of specific god beliefs [including Yahweh].