Trust your gut, don't listen to some rando. I edited videos professionally for a while, but that by no means makes me an expert. I guess the AI angle didn't pass the smell test for me. If you made the video it would be way easier and cheaper to make a small change in the original project than run it through AI to change one small thing that's on screen for a few seconds.

But if you have gone through it frame by frame, or as close as youtube allows, I'd be inclined to trust your assessment. I can think of half a dozen reasons they might use AI instead of rediting it, the top of my list being someone did it who was not a video editor or the original files were lost or not provided by the third party vendor that made the original.