How is this a Draw for insufficient material?


You lost on time. Lucky your opponent didn't have a pawn left or you wouldn't have gotten a draw. I'll get the article for you....

A draw by insufficient material is a draw because your opponent does not have any material to mate you with, thus it is declared a draw.
For more information, go here:
https://support.chess.com/article/268-my-opponent-ran-out-of-time-why-was-it-a-draw