It's a pretty well known rule that you can't win on time if you have insufficient mating material. You can only draw.
What's going on?

You did not have mating material. So a draw is the best you could do with even unlimited time. He had mating material but could not execute it in the specified time therefore draw. Your scenario would award a win to the faster player when both had only Kings left and one ran out of time.
Only kings left would be a draw too. No more playing would take place.

yea, if winning side runs out of time but only has a lone king (and maybe a N) the game is drawn. the logic goes like this: if the game were played out, the player with overwhelming material advantage would win, but instead he's penalized for not finding the win in time. :)
Good explanation.
can someone explain why: I was playing a 10 minit blitz game it came to the endgame and he had his king and rook and i had my king left he had 1 minit left to mate me and he failed so when his time ran out it said draw by insufficient mattirial, why was this not a time victory for me? as that is what i was playing for when i realised the time he had left and i was down mattirial.