Maybe you are right and everything was legit. It was a meaningless game to Surf A and a must win game for Surf C, so maybe Surf C rose to the challenge and Surf A just didn't care. All teams have bad games, and we see the better team lose (especially in soccer) all the time.
But let's be real on the facts. Surf A lost once in the 23 games of SCDSL league and CRL combined, with a 50+ goal differential. Quite simply, they very rarely lose. Surf C had a losing record in both SCDSL and CRL, winning 8 games over the same 23 total games and with a -19 goal differential overall. Surf A is phenomenal, considered by everyone to be one of the top 3-4 teams in SoCal at this age group, and has a legitimate chance to win National Cup this year. Surf C is a nice team, but I doubt anyone would consider them as likely to even make it to semifinals of National Cup. I really hope what happened was legit, but it has to be considered highly suspect at the very least.