The difference between atheism and religion is a belief in the super natural. Religious believers also believe in mother nature but believe its controlled and manipulated by a supernatural force they know as god. And that is where religion comes in. It’s the formula by which believers learn what god expects of them so they can act in a manner which pleases god and gets them rewards and avoids punishment.
Belief in these particular gods and their resulting religions are passed down from generation to generation. And they are usually geographically centered. Years of worship have resulted in codified behavioral manuals known as sacred texts.
Atheism on the other hand specifically excludes a belief in the super natural. Atheism has no other beliefs.
But many atheists have similar beliefs. Not because they are prescribed in a sacred manual but because we all look at the same information and come to similar conclusions. The universe is vast and no one has access to all the information that exists. But we don’t have to see all of it to come to valid conclusions. We just have to see enough of a broad range of topics in order to form statistically relevant conclusions.
That’s why so many atheists think similarly. Because we look at the same information and come to the similar conclusions. That is not a teaching of atheism. It’s simply the result of observation and thought from minds free of supernatural beliefs.
Religion is a system of thought based on the teachings of a supernatural entity. Atheism is the belief that there is no supernatural. Atheists believe what we believe not because of some atheistic book or belief manual. But because it’s what is left when you strip away centuries of supernatural influence on human thought.
Atheism is not a belief system, though all atheists have belief systems. Lack of belief in the super natural is the only mandatory belief necessary in order to be considered an atheist.
Atheism isn’t a religion because it lacks the one thing all religions share, a belief in the super natural.