I really have a distaste for Olympiad stuff, the whole sort of “culture” around it isn’t very appealing to me. Granted, I’ve only ever read about (people involved in) them and never even considered competing. But I dunno, that’s just a personal thing.

That said, the idea behind the solution is really neat, it’s sort of a fusion of analysis and combinatorics, which is really cool. I didn’t watch the whole thing and sorta skipped to the “main idea” of the solution, but I should probably watch the whole thing because it is an interesting solution. I don’t have much experience in problems like this, so maybe counting lattice points is something of a standard technique for a weird sum problem