Those who hold to beliefs would consider them truths. Depending on the strength of belief, some who hold to such beliefs would perhaps regard them as unproven truths, but truths nevertheless. Those who hold contrary views would of course dispute that the beliefs are truths at all.
In scientific terms, a theory is really a hypothesis that has been shown to fit the facts and which has predictive qualities. By that definition, and without devaluing belief, not all beliefs would be regarded as theories.
The answer to this question may depend a little on the context. In some belief systems, the belief would be regarded as true by adherents, even though some of its teachings may not correspond with known physical reality. This does not affect the faith in such cases because the truth of the particular religion is not affected.
Some scientists, indeed many display a similar belief in evolution which they maintain, even though there are many known and proven facts of science which contradict their belief, many of these discoveries being made by committed evolutionists themselves. Such details are also ignored or explained away, such action being contrary to stated scientific method which would indicate that the proven evidence should direct inquiry, rather than a belief in a particular framework.
In situations where beliefs are contradicted by known facts, they are hardly worthy of being called a theory, but perhaps, in scientific terms, an unproven hypothesis. In religious terms the Christian faith is particularly dependent on particular events being historically and factually true in an empirical sense, even though there are matters which are also beyond the realm of empirical verification. This is probably why opponents of the Christian faith expend so much energy in attacking the historically stated details of the Bible documents in order to demonstrate the alleged falsity of the whole system.
In this case one belief is used to attack the basis for the belief of another. The question here is what the facts actually are. These will not change regardless of who is right. If the Christian belief is truth in an absolute sense, it will reflect reality, and the facts will bear it out.
What then? are we better than they? No, in no wise: for we have before proved both Jews and Gentiles, that they are all under sin; As it is written, There is none righteous, no, not one: There is none that understandeth, there is none that seeketh after God. They are all gone out of the way, they are together become unprofitable; there is none that doeth good, no, not one. Their throat is an open sepulchre; with their tongues they have used deceit; the poison of asps is under their lips: [ROMANS 3:9I-10-11-12-13.]
The ci vilized live in a: Believed to be, Theoretical reality, in which there is: No right, No wrong; anly a relativity of poit of view!
And I, brethren, could not speak unto you as unto spiritual, but as unto carnal, even as unto babes in Christ. I have fed you with milk, and not with meat: for hitherto ye were not able to bear it, neither yet now are ye able. For ye are yet carnal: for whereas there is among you envying, and strife, and divisions, are ye not carnal, and walk as men? [I CORINTHIANS 3:1-2-3,]
Beliefs and theories, are among the more divisive practices of ci vilization, because they are not trths!
truth: That which dies not change, and once found will change all things!