So, I just played a Blitz 9x9 under Chinese rules as black. I won by resignation. I have an inkling as to why, but was a little bit surprised at my opponent’s forfeit. As I’m not sure exactly what I did to make white think that I could beat the komi, I’d like some input. They say you learn more in defeat than in victory - this is one of those times where this is definitely true.
Somebody please tell me - why did I win, and should I have won so early in the game?
I think that your second living group (upper right) greatly limited white’s options. Your lower territory is quite solid owing to starting on the 3-3 point (not something I’d do, but it works), and so white is unlikely to make a comeback, as it were. It would be quite difficult to make a fourth living group on a 9x9 board.
Just my thoughts as a 18-17 kyu 
My guess is that white tilted after failing to properly kill your corner group and resigned in disgust. A resignation was unnecessary in my estimation, as it’s still a favorable game for white even if that group lives.
yep I would agree with this
Yes, white can win simply by reducing black’s area on the left with normal endgame moves (I think starting with C8) and so should not have resigned after black’s group becomes alive. The score likely would have been close, with white winning after komi.