69 Kg1 Kd1 70 Kh2 Bd4 71 Kh3 Ke1 72 Ne4 Kf1 73 Ng3+ Kg1 74 Ne4 Kh1 75 Nd2 Bg1 76 Ne4 Qa5 77 Ng3#
A series of legal moves exists that leads to checkmate, so you duly lost on time per FIDE Laws of Chess.
Simple answer: White still has a knight, If you captured the knight, you would have drawn him after timeout, as white has a lonely king on the board.
