Results must be posted prior to the end of the Round. There is a Countdown Timer on the Home Page that shows how much time is left in the Round. It appears that your opponent posted the win before the Round ended.
Rule 2 states:
POST OR YOU’RE TOAST – If neither player is reported as the winner by the posted deadline, then both players are instantly eliminated. There is no excuse for failing to report a winner on time. Even if the games remain incomplete, one player must log in and post a winner in order to prevent automatic double elimination. Obviously, it is best if both players agree, in advance, as to the criteria (e.g., highest scorer, current leader, faster player) for determining which player should advance in the incomplete round.