Look at the teams above them this week:
#3 Oklahoma has to lose for OSU to win
#7 Baylor lost
#8 Ohio State plays #10 Michigan
#6 Notre Dame plays #9 Stanford
So, after one week, they are likely no worse than #7 if there are no other upsets.
The next week: Iowa plays the "other champion", Michigan/Michigan State/Ohio State
At this point, with half the teams above them having a loss, they are no worse than #6 -- and they likely jump the Big 10 team not in the championship game (if they didn't lose a second game already) making them #5. This leaves it for the committee to decide between Oklahoma State and Notre Dame -- just depends on what factors the committee deems important.