They could start by verifying the address of the house they're raiding. Way too often this doesn't happen and the police murder someone because they got the wrong house. They should identify the occupants of the house. The victim in this case had been swatted before and he had already warned the police that could happen. The swat team should have been skeptical going into this situation and taken the time to verify what was going on first. The call they got in this case claimed to be from the victim who said his father had shot his sister and he was hiding in another room. Even if the 911 call had been legit, the police would have shot the person who called for help and not the father, because they didn't bother to identify who they were shooting or who else was around when they sprayed bullets around the room from outside. They should have identified themselves as police. There's no reason not to. They should have at least attempted to use their big boy words before they started shooting up the place.

The very smart and obvious thing to do would be to announce themselves loudly on arrival; all squad cars have very loud speakers on them and most police departments have at least one armored vehicle specially for high risk situations. Breaking in through a bathroom window and then running around the house with guns drawn is a recipe for disaster. If this kid had had good pistol skills (not that unusual unusual in the US) it might just as easily have ended with one or both of the cops getting shot.

Police in many jurisdictions will just walk onto your property in pursuit of a suspect and get mad at you if you open a window or door to see what the hell is going on outside your home.

Identify themselves as LE, and of course physically represent as such, unambiguously, then demand the person put down the firearm. "Active Shooter" has no meaning just because the word is used. Also consider what everyone long forgot and few pay attention to; officers are paid, not volunteers. Risk is part of the job. You cannot shoot everything you think might be a threat. One can also question the quality of the system that handles emergency calls, or that responds to them. There are lots of guns in America. And lots of people who can say the words "active shooter". And often enough, phones and other objects are conveniently interpreted as guns, so I am not convinced that is the most important variable. Did he point it at the officers? If so, were the officers in proper uniform?

Now, if I were to answer your question, I would say it first depends on circumstances. I have encountered many people with guns. But if I was and active officer and encountered someone with a gun, I would do my best so that the encounter was arranged in a manner that gave me some advantage and at least a second or two to think before acting. Sometimes, mistakes are made though, and they always will be made. But the fact someone had a gun is no excuse.