Draw by insufficient material?

I played a game and was down on time so I exchanged some rooks for minor pieces & pawns to leave my opponent with K+B vs K+B+pawns. I still got flagged for a loss.

Because if you play very stupid, you can use your own pawns and bishop to trap your king and get mated just by the bishop.

Given the pawn positions it has to be pawns promoted to knights.

(here is the game)

Woops

http://en.lichess.org/80myacte/black