To be fair to your opponent It's not the most obvious win. It's a 5 minute game. And if black makes "nothing moves" that are not hard hitting then white has mate in 3. My guess is they only looked at maybe knight takes knight as a continuation forgetting that they have a bishop, or moving a rook to d8 to add defense to the knight. Both of which are way worse for black. If it were white to move then blacks position is bad enough to resign. Interesting position anyways.