Why does black win this game by time? Shouldn't it be a draw?

damnit it doesnt. wait 1 sec, i will write them down.

If White underpromotes to a knight and gets the king in the same colored corner of the bishop with the knight next to it, it is possible to checkmate.

imagine:

king H8 - king F7
king H7 - king F8
king H8 - bishop g5
pawn H7 - bishop f6 #

edit: from this position lichess.org/analysis/8/6K1/4k2P/8/7b/8/8/8_w_-_-_0_1

But pawn was already on h7 in the game

It is not a mistake. There is a way to checkmate. If the pawn promotes to a knight then you can checkmate with a bishop and king.

Omg yes! And it only works if you check with the bishop adjacent to the king. This is wonderful! Thanks, guys!

#12 #15 Yes thats it