Really riot..

Yeah, why not? They were ranked high Gold last season and the MMR generally carries over (with a bit of a soft reset).

Edit: Actually, their MMR is higher than yours, and they didn't do too badly in that match (relatively...your team as a whole got stomped). The bigger balance issue, honestly, is you in that match since they all had higher MMR on both teams. I'm guessing there weren't that many people on at the time or something.