Unlike the rook pawn, a knight pawn on the seventh wins: the defending king cannot shuttle between two safe squares, so the attacker's king has time to arrive.
Compare this with the previous drill. The pawn is on g7 instead of h7 and the knight protects it from e6. The black king, on g8, cannot stay put; it must step to h7 or f7 (not f8 or h8, both covered). From h7 it attacks the pawn, so the knight must keep protecting it, but now Black is not blockading the promotion square: g8 is free and the pawn can promote the moment the black king leaves the g8/h8/f8 trio.