Atheism is a belief. You have a belief that there is no supernatural being or power. A lack of belief in anything is agnosticism, not atheism.
If you define religion as a belief (I would) then there you go. If it's a set of practices and dogmas, then technically Christianity isn't a religion and it's denominations are as they practice things differently and some have added dogmas or different interpretations, even though they believe in the same God and have the same fundamentals.
Then I'd have to assume your religion is also not-believing-in-unicorns and round-earthism, as well as humans-need-oxygenism.
Agnosticism is not a lack of belief, it is a stance that one doesn't know whether a god exists or not. Frequently, the "belief" would be that it's impossible to know, which, by your definition, would also make it a religion.
It's amazing how often Jesus freaks will assert they know about other groups and then get their information 110% wrong because they only learned what their in group says about them
Nice irrelevant question, I'll answer it just to show that I know what I'm talking about because I'm actually part of the group being discussed, not some outsider pinning definitions on things incorrectly:
If there is/are they have 0 impact on the world as we interact with it by my own observations so I live as a gnostic atheist, though if any actual proof were ever to show itself I wouldn't exactly be shocked to find there was something beyond our comprehension out there
You would only be partially correct, as previously explained
I do not actively believe there is a higher power, so I am atheistic
I am open to the potential, so a fairly accurate simple description would be "agnostic atheist", or "someone who doesn't know whether or not there's a higher power and lives assuming there is not"
You'll notice that despite atheist being in there I've not only not made the positive claim that there's no god, I'm even open to the idea of something of that nature existing, because that's not what atheism is about