They changed the elo to rank mapping, so instead of say 1600 being LEM, 1600 is now GNM and LEM is 2200 (for example). Thus unless you were top of GE and didn't move down (eg you were at 5000, GE was at 3000 and now is at 4000) then you should have moved down.
If you didn't move down, then just be thankful because that's probably a glitch XD Although theoretically you could have just had some crazy lucky games and stolen enough elo to "stay" at your old rank, but that's super unlikely (since you aren't actually keeping rank but instead you are actually ranking up).
I won 3 games, and it pushed me down 5 ranks (DMG ->GN3) ^^
Also even though volvo said that mm is purely by elo not by rank, has anyone actually seen people +-5 ranks playing against them? I've only seen people within 1 rank of me in any game. That seems super unlikely.