Im an atheist myself, though I'll agree, the universe having a beginning does not preclude the possibility that it was created by an intelligent entity of some kind, a simulation is one way this can occur, but not the only one. I dont think such a creator likely, but I cant rule the option out. However, I dont think that an entity like this is really deserving of the title of god, because a simulator (or someone who has some kind of weird tech to mess with spacetime such as to create a new physical universe artificially) is still just as fallible as any other limited entity inside their own universe. Conceivably, if someone discovered a way to cure aging or something within the next few decades, its not impossible tho probably very unlikely that you or I might someday see the technology to create such a simulated universe developed, but if I were to create one, that would not really change what I am at all, or give me limitless knowledge or make me deserving of worship. This might be because I was raised in a family mostly full of Christians and therefore interpret the word the way Abrahamic religions do, but I dont think I could really consider anything less than an actually Omnipotent, Omniscient and therefore limitless and infallible being to be a god, and as I also believe that omnipotence is a logically impossible and self-disproving concept, and therefore, that it cannot exist in any reality no matter what rules may govern it, I feel as certain as I can be of anything that no such thing exists.