Because of this, we can rightfully say that religion means, simply:
a set of beliefs concerning the cause, nature, and purpose of the universe.
What is interesting is that atheists are full of such beliefs in science theory, which has not been proven to be fact. Thus, atheism is definitely a religion.

Your statement is that religion is a set of beliefs concerning the cause AND nature AND purpose of the universe. Logically if any of these are not true, the statement as a whole is not true.
Atheists do not posit a "purpose" to the universe (read
https://en.wikipedia.org/wiki/Teleology).
Therefore your statement as a whole is not true, and atheism cannot be considered a religion by that definition.
Actually, the truth doesn't have anything to do with what atheists posit. Since for many atheists, religion is something that they are against for themselves, they simply have a religion of non-religion. I admire how faithful many of them are, that they would continue with their religion of non-religion when all the while they are being shown that they have a religion. Their choice, I guess.

You just ignored everything I wrote there, so let me bring you back to the conversation.
1. You state:
Because of this, we can rightfully say that religion means, simply:
a set of beliefs concerning the cause, nature, and purpose of the universe.
2. I explained that atheists have no beliefs concerning the purpose of the universe.
3. Therefore your simple definition does not apply to atheists.
Are you changing your simple definition or will you ignore a logical argument?