I'm not sure what would or would not qualify as an "ontologically basic mental entity". I'd need to look it up if you wanted me to tell you whether something does or does not deserve to be called "supernatural".
I'm not sure I'm understanding your lack of understanding, but I hope this addresses it.
An ontologically basic mental entity is something which can think, but can't be divided into smaller parts which can't think. If, hypothetically, there were a fundamental particle which had thoughts and intentions, which could not themselves be caused by interactions of smaller parts within it, that would be an ontologically basic mental entity. More to the point of what people postulating supernatural entities actually have in mind, if there were a such thing as souls, which could think and feel, but the thinking and feeling weren't the result of some process within parts that the soul were made of, such that you could separate those parts out and not have them be involved in thinking or feeling anymore, then those souls would be supernatural.
As such, any beings simulating our own universe, as long as their intelligence were the result of a process among parts rather than a fundamental quality of some indivisible aspect of themselves, would not be supernatural.
The 2012 LessWrong Censur had a question about belief in God. It also had a question about how people self label their religious beliefs. Interestingly 6.69% of the nonspiratual atheists believe that it's more likely that a God exists than that no God exists. On the other side of the spectrum 17% of the committed theists believe that the chance that God exists is only 2%. Those 2% are the median for nonspirtual atheists who belief in God.
Not a single person who took the LessWrong census believes that the chance that God exists is less than 1%. Given that this community has quite a lot of contrians and quite a lot of skeptics I would have guessed that there are people who believe that the chance that a God exists is less.
The orginal question on the survey was:
The numbers make also a nice plot:
There's also the question:
Given those results what do you think if someone tells you that they are atheist or a theist?