Are all Atheists really just Deists?

I had an interesting discussion with my roommate and best friend the other day about whether or not Atheism is truly just a theory. I suppose I must preface this by saying one cannot truly know what everyone else in the world firmly believes, because often one isn't even sure what they believe in most of the time.

So Atheism, for this sake I shall call it a theory, by all dictionary definitions, not a cultural American definition, is defined as the rejection of belief in the existence of deities (shoutout to wikipedia for these). Now, if we are to accept this as the definition of what an Atheist truly believes then let's go forth to the definition of Deism. Deism "is the standpoint that reason and observation of the natural world, without the need for either faith or organized religion, can determine that a supreme being created the universe. Further the term often implies that this supreme being does not intervene in human affairs or suspend the natural laws of the universe." So, really in essence Deism is the belief that there is a POSSIBILITY, regardless of how trivial or minute this probability is, from .000001% to 99.9%, that there is a supreme being.

Now, I have always regarded myself as an atheist. But really in essence I cannot rule out completely the existence of something that controls the universe. No one can. No one can say for sure that there is not a god, just as no one can say there is a god. And by 'god' this does not insinuate there is a person or a sentient being controlling all. Not by any means is this what a god could be. Our bodies are made up of so many particles that replicate millions of times and fail so infrequently, and our body has time to correct this, that it is seemingly perfect. Now, this can be attributed to nature or evolution, sure. But if we have so much in us we don't understand, it really isn't possible to rule out that we don't have the capability to fully fathom what is beyond us, or what is in other dimensions.

I used to use the old atheist argument that if there was a god, who created that god? And so forth and so on. But to use this argument is to say that our brains can understand infinity, and really we cannot truly grasp just what infinity means. To believe in the existence of ourselves we must accept that there truly could be no beginning to the universe or what it really is, because something, SOMETHING, had to come around to make the universe. Wrapping your head around that can make one go nuts.

So, if deism is defined as entertaining that there could be something in this universe we do not comprehend, which clearly there is, then we must say that atheism is not a practice, but a theory. There are things beyond the control of humans in this universe that happened without us and will happen for eons after us. Maybe Jesus Christ didn't rise from Hell after sparing humanity by sacrificing himself three days previously, but certainly it cannot be DISPROVEN ever beyond theory that maybe there is a man upstairs, however unfathomable it may be.

Edit*: I suppose I should add that I do believe that Atheism has turned into a cultural term for those who generally disbelieve in a 'God' such as a higher power. But this cultural term is mislabeled, because truly no one can rule out the existence of anything. Therefore, agnostic or deist may be a more suitable term than atheist for nonbelievers.