BOTH Kansas St and Iowa St would win the 3-way tiebreaker section b (record against common opponents).

In the description for multi-team tie-breakers it says “If at any point the multiple-team tie is reduced to two teams, the two-team tie-breaking procedure will be applied.”

This could be interpreted in this scenario that the tie-breaker was reduced to just two teams (KSU and ISU) since they are both tied and beat BYU in that tie-breaker. Even so, it’s possible that KSU and ISU would have the two way tie breaker, which KSU would win, then maybe they would redo the two-way with ISU and BYU? I’m not sure.

I could also be interpreting it wrong and they would not declare KSU and ISU as joint winners of the 3-way since maybe only 1 team can advance out of the 3-way. It’s not very clear to me.