SE should have access to logs for these matches - it should be easy to investigate. If They find these guys had games that generally only lasted a minute, where one side did close to 0 damage/healing and threw the matches repeatedly, it's pretty obvious they were just boosting their ratings. The way that guy one shot up in rankings it seems like they just swapped him back and forth and had whatever team he was on win to boost him up, but either way this should be easy to look into.