No? Not even close, it clearly states it's a refusal to believe or accept something as true, it doesn't mean your position is that god is 100% not true, atheism position is: You don't have enough evidence, therefore I don't believe it.
But we are taking about atheists/religion. Even if non-believing something simply put the non-believer into a vacuum regarding that subject, the mouthy atheists especially have beliefs. And they have beliefs about God and all kinds of things regarding Him. One of those beliefs is that they don't know that He doesn't exist... or is that part of their knowledge, and not part of their belief system?
Even if a person could hold a position of non-belief regarding God, He would only be making himself into God by holding that position. Why? Because He would be attempting to defy the natural and scientific knowledge of God that is all around him.
This means that he still has religion, no matter how angry at this fact he gets.
Well, the definition of atheism doesn't include the word religion, so it's not a religion.
''One of those beliefs is that they don't know that He doesn't exist..'' And again, atheism is not the belief that god doesn't exist 100%, it's the non belief in the evidence presented to support god. Ghosts might be real for all I know but right now I haven't found evidence that they are, I also can't say they are 100% not real but I can't believe in them right now. That's what atheism is.
Probably very few definitions include all instances of the defining use. Definitions attempt to be brief enough, yet inclusive enough, so that people who use them can understand the other things that they cover which are not listed in the definition, itself. This is part of the reason why languages change with use, over time... because the definitions are not inclusive enough.
Oxford says that non belief is lack of belief in something, especially religion - https://en.oxforddictionaries.com/definition/non-belief. As I said, just because someone doesn't believe something, doesn't make him a vacuum regarding that thing. Lack of belief in something is simply believing that it doesn't exist. The consideration of "it" is belief in it enough that the non-believer considers it. Lack of believing that atheism is a religion, is simply lack of looking at the definition of religion entirely.
In other words, imagine a person and a church who has never heard of the word religion. Yet they practice it on a regular basis in their church services. Just because they haven't heard the word, doesn't mean that they don't have religion.
Atheism falls into the pattern of religion, even though many people want to deny it. The fact that they look at the word makes them religious in their observation of the word. Talking about it, even in a negative and negating way causes, at least, simple belief in it. The closest that you can come to an atheist is someone who has not even considered the subject of God, ever.