Phony Benoni: I wouldn't expect a game from an U10 section to end on time forfeit this early. Of course, these are not your average U10 players (though surely those ratings are not correct).
365Chess shows the same result and game, and has Dzagnidze winning the tournament (8-1) with Muzychuk second (7-2). Wikipedia confirms that Dzagnidze was indeed the tournament winner, so I think we can count the result as confirmed. Also, looking at the earlier pairings makes it evident that the colors are correct.
Most likely, this is a scoresheet error; either it's incomplete or contains an earlier mistake that made the later moves unplayable.
Incomplete looks like a strong possibility to me. Scanning the games from this tournament at 365Chess reveals a large number that ended abruptly. Also, while I think White must lose some material to stop 18...b4, a line like 18.b3 Bxa1 19.Rxa1 is not the end of the world; Black's king position is a bit open.
It may also be relevant that Muzychuk was only seven at the time of the game, young enough to win the event twice in the next three years.