Just like not believing in bigfoot is a "belief", and just like not believing in purple dragons is a "belief"
It's not at all the same. Personally I'm not really a Theist, if I believe in a God it's something like
Parabrahman. But there is certainly evidence that all of this is not simply "matter". For one, that is just a one-sided philopsophy, a Materialist position is no more tenable than an Idealist position. Reality cannot be explained by any particular philosophical position, it is beyond such conceptual projections. But the notion that there is some kind of "higher power", at least that there is something other than matter, can be demonstrated.
If you look at your own mind, you discover that you are a conscious being, experiencing things as a subjective entity. Now, how can matter create such experience? If it were nothing but an aggregation of molecules, it could not. It could create functioning machines which behave like human beings, but it could not create conscious experience. Well, it could be that everything is conscious, one could take a pantheist position, but then why is consciousness individual rather than collective? In the first case, it begs the question of when matter became conscious? What is the point at which mere mechanical existence becomes living and experiencing existence? In the second case, there is the question of why and how consciousness is individual rather than collective?
It may be possible to create an artificial intelligence which displays all the characteristics of human beings, however it would not be conscious. It would not have (using a rather ill-defined term) "qualia". In Buddhism, the ground of consciousness is compared to "clear light". You may reach the point of explaining, categorizing, mastering, all physical phenomena, but you cannot explain the existence of that "clear light", which manifests as subjective experience with the creative play of thoughts, without abandoning a purely materialist explanation of the universe. Idealism puts too much emphasis on subjectivity, and cannot clear explain the objective universe, while Materialism places too much emphasis on objectivity and cannot explain the subjective universe.
From recognizing the existence of consciousness, theists develop a notion of "soul" or "spirit", and posit the existence of an Ultimate Being who is the source of such experience, like a fire giving off sparks. I would not argue with you if you were to say that such an anthropomorphic deity of judgement is an aberration, however the concept of an Ultimate Being in and of itself is not so illogical. In any case, consciousness itself could be considered a kind of deity, Buddhism speaks of a primordial Buddha known as "Buddha Unchanging Light".