Who knows. I looked at your last 3 completed wins and saw 1 guy who quit after like 5 moves ... life happens, maybe his wife needed him to go clean out the garage or something. I saw one where you had a rook and a win in a few moves at endgame. I saw one where the other guy threw a piece away and quit in disgust (this guy should have probably played on: beginner on beginner both sides hang pieces usually and no sense in quitting after the first one). At higher levels a lot of players will quit after losing a piece with no good counterplay for the loss: they respect that their opponent can probably win a piece up, and that is true at some point.
Anyway, take your win and move on. It happens, and unless they say something, no way to really know why.
I don't know if some awesome people have multiple log in, because i noticed while i sock that many resign after a few of (my monster moves) moves, are they trying to help me raise my score? but thank you