As of this writing, the question concludes with the following paragraph:
I'd like to conclude by respectfully reiterating that, on one hand, the author seems to be reliable, and on the other, even in the case there's a fatal mistake somewhere, I'm sure it will be found agreeable that we are only human and it happens to everyone, so no harm done for him as long as it is caught and acknowledged quickly (I wouldn't want to put undue pressure on him with my question).
In a comment, the OP also says this:
I'd prefer to not expose the author of the preprint to too much pressure in the early stages of his career. As long as he rectifies the situation (e.g. by withdrawing the preprint in a timely manner), he should move on and be given every opportunity to prove himself in the future.
In my mind, the fact that the OP feels the need for such disclaimers is a bad sign. It suggests that social factors are playing a heavy role, to the point where they may be interfering with free and open discussion of the actual math. Longtime MO users will recall the decision made in the case of Atiyah and the Riemann Hypothesis. While the situation with the current question is not quite the same, I think that it's generally a sign of an inappropriate question if people feel the need to issue heavy disclaimers. Indeed, the OP seems to feel similarly, and plans to delete the question.
Now, initially, the question did not have these disclaimers. The first version pretty much just asked, "Is this paper correct?" and as such seems like a clear candidate for closure, per MO's usual policy. Later versions added some specific mathematical content, and it looked like it might be headed toward an acceptable MO question, but in every revision, the main question was still "Is this paper correct?" and not the actual math. I think I would have voted to close every revision.
Having said all that, I think it's still possible that this question could be turned into an acceptable one, if the "Is this paper correct?" part is deleted and the focus is on a specific mathematical claim in the paper that turns out to be subtly wrong. I can imagine something along those lines that would not require disclaimers of the form, "No offense; I know you're smart and all, but..."