How does the 'Won on Time" rule work?

How does the 'won on time' rule function? I took an opponents Queen and I'm pretty sure I was ahead on points when suddenly the computer announced that my opponent 'won on time'. An explanation of the rule will be appreciated.

The points thing is nothing but a guide, you can be up on points but losing the game.

If you have enough material to checkmate and your opponent runs out of time you win, no matter how badly you are losing on the board. If you don't have enough material to mate (lone king, King&bishop, King&knight) it's a draw.

famous example of why points means absolutely nothing in a won position^ but yeah the agreement at the beginning of every timed game is : if i run out of time i forfeit. 

I was leading the match, and had 2 min. 11 sec. left. Then it was interruptet. Half an hour later, it was the same. Then I checked my game, and have lost by time. carstennielsen