could be defined in different ways. If theism is defined as a belief in god/s that are supernatural in nature, the 'a' in atheism means "without"... so it could simply mean non belief in supernatural gods, theories or stories related to theism.

Many people do not believe in magic, miracles or superstitions on a more selective basis... but most do not go around calling themselves a-superstitionists.

Many have likely heard many stories and theories about gods, Santa Claus, leprechauns, fairies, angels, ... but likely most don't literally believe the stories are true. Doesn't mean they might not find some value or benefit to at least some of the stories, however.

While many may be content to describe themselves as theists, atheists or as agnostics, others may not wish to place any such labels upon themselves, as they may not feel they can possibly 'know' that supernatural beings or events actually exist or do not exist, however one defines the term 'supernatural.' And since 'natural' knowledge has often been obtained about heretofore unexplained events or phenomenon that were previously considered to be miraculous or supernatural... that sorta takes the 'supernatural' out of previous beliefs for many... so someone who was a previous theist or believer might well become an unbeliever in theism... not that there aren't still many mysteries in the universe that we still do not have knowledge of.

One might just assume that everything in the universe is natural (whether explained or understood or not) rather than supernatural. Perhaps you could call them a naturalist, or someone who believes all things are natural or come from nature?

And instead of theists, you could just call them a supernaturalist, or superstitionist?... which would seem more accurate terminology, IMO. Otherwise, you get into really "arrogant" assumptions or territory when you start talking about god/s and such, and which ones exist and which ones don't exist..... and which ones inspired this book or that.... or not....