Quoted from the Big 12's website (link below):
"Isolation – Regardless of vaccination status, individuals with a confirmed positive test must be isolated for five days. A negative test anywhere between days 6 to 10 allows for the return to activity."
Effective immediately, the Big 12 Conference has adjusted its COVID 19 medical protocols in the following areas:
The BIG 12's protocols don't differentiate between unvaccinated or vaccinated. Based on how I'm interpreting this, they had to have tested positive.