Trump is obese, there's no doubt about that. But I agree that the definition is probably out of whack. I know what weight I'd have to be to not be obese, and I know how skinny I am at that weight. I was it once. No way that's my "normal" weight.
If you look at photos of the man from the 2016 primaries to the present he actually looks in better shape, not as puffy, now than back then. The presidency usually ages the occupant rapidly. But Trump seems to be thriving on it. Certainly doesn't look like your average 74 year old.