The two teams, big furious joke and sup fresh our turn baby, an RLS (Rogue, Warlock, Shaman) and a RetPR (Retribution Paladin, Priest, Rogue) respectively, are composed of members who have performed consistently well through different Arena seasons. The Rogue of big furious joke, Nutzz, is rumored to be the legendary Neilyo, who grew to infamy with his popular series of PvP videos. Its Shaman, Douja, formerly played pro for Team Pandemic. The other team's Paladin, Euneek, topped his Battlegroup last season using the Holyplay (Ret Pally, Priest, Shaman) comp. None of these guys are slouches and aren't likely to have win traded the way teams in the past have in order to reach the hard cap.
Their recent achievement has brought the current Arena system under scrutiny, as Blizzard has stated before that they never intended for players to reach the rating ceiling. Considering the system has undergone numerous changes in the past few seasons, it's not unreasonable to think that it's due for another overhaul. Regardless of the system, a 3k rating is an incredible achievement. Congratulations on jobs well done.
[Thanks to cigarillo for the heads up!]