Yes, but there are highly probable alternate explanations (other than the truth of Christianity) for their belief in Christianity, so the fact of their belief is very weak evidence for Christianity.

Of course, there are also perspective-relative "highly probable" alternate explanations than sound reasoning for non-Christians' belief in non-Christianity. (I chose that framing precisely to make a point about what hypothesis privilege feels like.) E.g., to make the contrast in perspectives stark, demonic manipulation of intellectual and political currents. E.g., consider that "there are no transhumanly intelligent entities in our environment" would likely be a notion that usefully-modelable-as-malevolent transhumanly intelligent entities would promote. Also "human minds are prone to see agency when there is in fact none, therefore no perception of agency can provide evidence of (non-human) agency" would be a useful idea for (Christian-)hypothetical demons to promote.

Of course, from our side that perspective looks quite discountable because it reminds us of countless cases of humans seeing conspiracies where it's in fact quite demonstrable that no such conspiracy could have existed; but then, it's hard to say what the relevance of that is if there is in fact strong but incommunicable evidence of supernaturalism—an abundance of demonstrably wrong conspiracy theorists is another thing that the aforementioned hypothetical supernatural processes would like to provoke and to cultivate. "The concept of 'evidence' had something of a different meaning, when you were dealing with someone who had declared themselves to play the game at 'one level higher than you'." — HPMOR. At roughly this point I think the arena becomes a social-epistemic quagmire, beyond the capabilities of even the best of Lesswrong to avoid getting something-like-mind-killed about.