Yeah, it happens. I lost 11-0 on a streamed gambling match a few months ago, me being a 570 at the time and my opponent 590. Then I beat the opponent the next two sets (barely), and ended up getting the cash overall. A couple months before that I was gambling with a 603 and I beat him 7-0. None of those were on Solatto, but I could see the 11-0 and 7-0 sets raising flags. I've also beaten 2 700 level players an even set each, 20 years ago before Fargo. One gambling, one in a tournament. We've all been around this game forever, and low probably stuff does happen.
I think given that the OP is a regular customer of Solatto, as was his opponent (I know the OP personally and he showed me both player's games), the Solatto company should have dug deeper.
Also, what would the motive be to submit false scores or to dump, in "this" case? The OP would have his fargorate go up. That only helps his ego, nothing monetary. The opponent has 1600 games, and is a 657. He's already above nearly every single tournament cap by a large margin, and he's already the speed where everyone knows he can play and barely gets action. Going down potentially .5 or 1 point from this match wouldn't do him any good.