Why did he win and not a draw?

In that case it is true, I still think it's ridiculous. Though finally someone with a good explaination, thanks :)

Black could technically promote to a knight, and lose in this fashion:

en.lichess.org/analysis/6nk/8/6K1/4N3/8/8/8/8_w_-_-

Black could promote to a knight, and then lose.
en.lichess.org/analysis/3N2nk/8/6K1/8/8/8/8/8_w_-_-

It works with a bishop or a rook too, the queen is the only piece that can't block in the king without defending it at the same time.

Sure, it does seem a little ridiculous, especially since if you LOST the pawn it would be an instant draw. But you need a rule that doesn't depend on judging a position on how bad you'd have to be to lose it. I don't see a better way.

It just gets down to "get rid of your pawn" which is annoying since the point of the game is the direct opposite.

there IS a mate if the pawn promotes to a knight.