Why is White knight to f5 not an ideal move in this situation? As far as I can see, unless Black takes the white bishop with the rook, it's mate in 2.
Of course one forced mate is as good as another, but if you did want to differentiate between forced mates of different length, then an argument can be made that fewer moves is better. This is certainly how lichess does it in these puzzles, though it is certainly annoying if such a move is judged as a mistake. Sometimes you get an admonition that your move although good is not the best and that is less annoying though arguably also incorrect.