No, the context was the large animal was a threat. Under such circumstances, police can and do often kill large animals. However, if the owner of the large animal shows up with a gun, and threatens the police with it, if they kill his large animal, he is as much, or more threat as is his animal.
In either situation, if the owner had showed up and was able to control the animal, and did, it would be one case. However, the owner showed up with a rifle. He had no other way of controlling his animal at hand, and the animal was an acute threat.
But, in all fairness, let us consider the alternatives.
The police do not kill the bull, and allow the injured people in the Suburu to die because they are not attended to. The bull continues to attack any people on foot, or any vehicles that enter the area. It may even decide to attack the rescue helicopter.
None of these alternatives are tenable. Had the rancher held his temper, allowed them to kill his bull, he could have sued them in court, and likely lost. However, his bull is likely insured, so he would not be badly harmed with its loss.
Every account I have seen is that the deputies saw a man with a gun and went berserk. I have not seen one account that said the man was being difficult at all.
These people are animals. Much more dangerous than an injured bull! And they'll skate.