Why resign?
Nxc5 doesn't look that good. White can free his game by exchanging in the center. White is cramped and needs to be kept that way.
Black probably should push to d4. But in any event, white should not resign.
Just message the guy and find out why, it might not have anything to do with the game at hand, it might be something personal.
Opponent wasn't doing too well, but this was still far from losing