They probably figure that Oklahoma beats Texas Tech and OKlahoma wins some sort of tirbreaker and then they beat Missouri in the Big 12 championship game.
If Oklahoma beats Texas Tech in 2 weeks, and then all 3 (OU, TT, Texas) win out, it goes to a tiebreaker system to decide who represents the Big XII South in the conference championship. It’ll go down to the 5th or 6th tiebreaker, which is BCS ranking. If OU beats Texas Tech and then Oklahoma State, they should be ahead of Texas.
I wish the Big Ten and Pac 10 had conference championships.