Its because you ran out of time but your opponent didn't have sufficient material to put you into check.
FIDE Laws of Chess Article 9.6:
"The game is drawn when a position is reached from which a checkmate cannot occur by any possible series of legal moves, even with the most unskilled play. This immediately ends the game."
i was playing a 10 min blitz game, and my timer hit 0 at the exact moment i checkmated my opponent. in stead of awarding either of us the win, is said draw, due to insufficient material, which makes no sense at all. is this intentional or a programming glitch? could somebody explain this to me?
you can see the game here:
http://www.chess.com/livechess/game?id=465921716
as you can see, the move record shows i didnt make the final move in time, but it still says that the game was a draw.