I'm willing to give this officer the benefit of the doubt and call it an unfortunate accident. It is quite possible that he did not have a clear understanding of just what a cougar looks like, maybe he was a little nervous thinking that a feral cat would attack him, or, as some have stated, maybe it's time for a visit to the opthamologist.
Also, it is worth noting that the folks who called this in mistook it for a cougar. It's not as if Barney Fife went a-huntin' and blasted the first thing that moved, and it doesn't say that he sat down and discussed the situation with the caller before he went after the cat. What are you going to do if a call comes over the radio that there's a (potentially) dangerous animal behind location XYZ, and you suddenly spot what you think might be him? We're not talking about the kind of "oops" that gets a human being killed, we're talking about something that actually resembled the animal he was sent to find.
It was a mistake, plain and simple, and while it's unfortunate that fluffy had to be on the business end of the deal, it's not some great tragedy, and it's not a valid reason for anything more than a good solid smack over the head from the LT.
I do rather like the idea of training the officers in dealing with wild animals. I seem to recall that people are meeting up with wild animals more often now as that city moves into formerly wild areas. You should be prepared for the sorts of things you're going to encounter.