Something that sticks out to me as someone who works in 911 dispatch (rest assured, I think my cops are bastards) is that I didn't even hear him key up to give his dispatcher a heads-up first (I don't want to give him the benefit of the doubt but it's possible he did and I missed it, I had my volume on pretty low)
Luckily we haven't had any cop shooting dog incidents in my county while I was working, and the small handful I've heard of that happened on other shifts have been justified cases where a dog actually attacked someone, but what we do get is a whole lot of injured deer or other critters that have been hit by a car and need to be put down, and our cops always key up beforehand to let us know before they do it, if only so we're prepared if 30 seconds later we get a call about shots fired in the area. Ignoring how inappropriate his actions were in shooting the dog, this was definitely a situation where there was no immediate danger and he could have taken an extra minute to radio his dispatcher to give them a heads-up and let them send a message to the calltakers "in case of shots fired calls in the area, officer dickbag is putting down a potentially rabid dog."
Of course this douchenozzle has no respect for life, he doesn't even have basic courtesy towards the people he works with or the people in the neighborhood who might be startled by hearing gunshots. People are understandably very relieved when they call in terrified that they just heard gunshots and we can confidently tell them "an officer just had to put down an injured deer a couple blocks away, so that's probably what you heard" and it saves us from having to enter a call for it that they then have to acknowledge.
Side-note, it's mind-blowing to me how many people just ignore what they think are gunshots. I work in a pretty diverse county that has a little bit of everything, but for the most part it's just various flavors of suburbia, not exactly the hood where shootings are an everyday thing or the sticks where every other neighbor is hunting or target shooting in their back yard, gunshots should trigger some alarm bells for most people. It's wild how many people will mention off-handedly that they thought they heard gunshots but didn't call for some reason, or they wait until way after the fact to call about it. Now I'm also pretty sure 90% of them are probably misidentifying what they heard (we get so many people calling in shots fired for fireworks, cars backfiring, doors slamming, etc. sometimes I can hear the fireworks in the background whistling, sizzling, and crackling in very un-gunshot ways while my caller swears up and down that they "know what gunshots sound like,") but even still, that's one of those cases where you should probably err on the side of caution. I'm personally very willing to ignore a lot of things, but if I think I hear gunshots somewhere I shouldn't be hearing them, I'm calling 911 immediately.