Well, it would be nice if you were more specific, but probably you left/disconnected etc. and so, dotabuff has acknowledged, that you abandoned the game. I had once a similar situation- at the beggining i had con issues and reconnected, won, but found out, that dotabuff counted the game as my loss.
Per favore Accedi per inviare commenti.
http://dotabuff.com/matches/187418586