Chess.com, along with FIDE, awards the full point to your opponent if you run out of time, unless your opponent has insufficient material: not enough resources to feasibly carry out a win. This effectually concedes victory to both players, which is sensible since on the one hand, your opponent rendered you incapable, but on the other, you held him off until he had no time to finish you off.
However, Chess.com's definition of "insufficient material" differs from FIDE's Laws. Chess.com simply looks at your material. If you have lone K, KN, KB, or KNN, you have insufficient material. So in your case, your opponent ran out of time, but since they determine that you could not have checkmated him anyway, Chess.com split the point.
Whereas FIDE calculates all possible futures; if one legal series of moves results in checkmate against the player whose flag fell, flag-fall is a loss for that player:
Except where one of Articles 5.1.a, 5.1.b, 5.2.a, 5.2.b, 5.2.c applies, if a player does not complete the prescribed number of moves in the allotted time, the game is lost by that player. However, the game is drawn if the position is such that the opponent cannot checkmate the player’s king by any possible series of legal moves.
Just for kicks, let's see one of these legal series of moves wherein you checkmate your opponent.
[FEN "5Q2/8/8/8/2k2P2/6K1/4n3/8 w - - 0 0"]
1. Kg4 Kd4 2. Kg5 Ke4 3. f5 Nf4 4. f6 Kf3 5. Kh6 Kg4 6. Kh7 Kh5 7. Kg8 Kg6 8. Qe8+ Kh6 9. Kf8 Kh7 10. f7 Ng6#
That's why FIDE would count flag-fall to be a win for you. Chess.com does not. To be fair, that or any line resulting in victory for you is so far-fetched that in this case, it's hard to complain that you could feasibly have won.*
Sources: FIDE Laws of Chess, Article 6.9; Chess.com forums - list of threads with "insufficient" in the title.
*There are a couple positions, however, in which King and Knight can force a checkmate vs. King and Pawn. For example, there would be ample cause of complaint if Black purposely runs out of time in the following position:
[FEN "8/8/8/8/N7/p7/k2K4/8 w - - 0 0"]
1. Kc2 Ka1 2. Nc5 Ka2 3. Nd3 Ka1 4. Nc1 a2 5. Nb3#