Whether atheism is a "religion" largely comes down to semantics. I think it is less controversial to say that it is a worldview which is in direct opposition to the Christian worldview. Atheism can certainly be couched in religious terminology, but the argument that goes on between atheists and religious persons over whether atheism is in itself a religion is an argument over how you define the word religion. I think the author fails to identify that in his article.
Good point, thank you! I tend to define it in the same way I do all other world religions, but that's me. I can't speak for the author.