Theism is about God. One can believe in beings thrown up naturally with supernatural powers.
Indeed a belief that has an eternal self perturbed universe is supernatural since none of it can be proved naturally.
A theistic mindset is one that accepts supernatural entities, whether god (necessarily) or the many other supernatural entities and phenomena that are part and parcel of religions - such as angels, miracles etc etc.
While I accept it is possible not to believe in god but to believe in other supernatural things this requires a level of cognitive dissonance which doesn't sit easy with atheist thinking.
So if someone who was brought up as a Christian then rejects the religion of their upbringing, claiming to be an 'atheist', but being angry
with god and signing up to all sorts of supernatural entities and phenomena of the occult I think the pretty easy conclusion is that they aren't atheist, merely a rebelling and somewhat confused theist.
And don't forget that the occult is generally considered to be theistic. I accept that occultism isn't well defined, but in most cases it includes the divine, gods and other deities.