I do not know the details of this situation, but I will relay the experience we had in my area of MT:
The MT FWP biologist made a gutsy call when bighorns started to cough in a district here in the Bitterroot. They shot many, many sheep in a short period of time. In a nearby district at the same time, they took the standard "wait and see" approach, and lost a much higher percentage of sheep. The consensus here now is that the swift action in our area prevented a lot of damage.
It seems that wild sheep are very susceptible to pneumonia from domestic sheep and swift action can help. The cough has completely eradicated some herds of sheep in MT in the past.
If the sheep they killed were coughing, it was a good call, IMO.