For example. The atheism religion has people who try to (unknowingly) set themselves up as God by proclaiming (falsely) that God doesn't exist. So, when they try to set themselves up as God, they proclaim that He exists. In addition, many of them understand certain factual science. They understand part of what God created. So, even they have some minor accuracy in their religion.
Atheism (from the greek ἄθεoς, àtheos, composed of α- privative, without, and θεός, god, literally without god) is a philosophical position opposite to theism and pantheism in general, to polytheism and monotheism in particular. So, everyone who claims that atheism is a religion simply doesn't know what he's talking about.
Just because people make up a virtual definition and try to apply it to reality, doesn't make either the definition true, or those who attempt to apply it to themselves to be truthful.
Atheism is simply a religion that attempts to fight against God by claiming that He doesn't exist, while nature shows us all around that God DOES exist. So, atheism has formed itself into a religion of non-religion, because atheists are liars about their atheism.
A person who is really close to true atheism is a brute beast of a person... one who doesn't have enough sense to look at nature and see God... one who doesn't realize that he is missing God... one who goes on his way without thinking much, eating and drinking and finding a partner like himself to have sex with.