Transferred this here because this "it's not a bug" case.
Your opponent didn't have 11 eligible players so lost the game with 0-3.
In knock out games, because of this reason, he looses the second leg also with 0-3 (but you didn't play a 2nd game, it's only 1).
Now the game counts this game as a draw, not a win.
Why ? We don't know, we reported this but didn't get any answer yet.