Strange ending to game..please investigate this

Please look at this game...

http://www.chess.com/livechess/game.html?id=234276125

it is now white's move.  I (white) ran out of time at this position.  The message on the computer declared it a draw due to insufficient material, which I suppose I should be glad of since I rightfully lost on time.  However, Im puzzled to the computer's declaration of a draw due to insufficient material.  The win is simple from here...56. Qc7 Ka8 57. Ra6#. 

I should have lost on time.  But why the designation of a draw?

tex

In other words, my opponent has not earned a win on time since he can not mate me due to HIS insufficient material.  I would think that if you can evade an attack as a lone king long enough for you attacker to time out then you have indeed EARNED the win due to sheer tanacity.