It was purely the re-introduction of the B10 and PAC into the polls. Inserting Ohio State at #6, Penn State at #10, Oregon at #14, and Wisconsin at #19 explains almost all of our 5-position shift to #21. The last piece of that is the voters rewarding Mississippi State for knocking off the defending national champs by adding the Bulldogs at #16.
Meanwhile, only two of those teams affected A&M, because they started higher in the standings. Ohio State and Penn State pushed them down two spots, and they lost a spot because of their sloppy play against an inferior team.
So, net effect: we didn't get punished at all, we're actually up 4 spots from a pre-season #25 ranking (the last time the B10 and PAC were included), while A&M got punished just a little bit (loss of one spot for poor play).*
Go Vols!
* funnily enough, A&M fans could make the argument they weren't punished at all...since their pre-season ranking of #13, and their current ranking of #13, puts them with no net change from the absence and return of the B10/PAC.