Call me ignorant if you want, but IMO an armored SWAT team can wait to see an actual weapon before opening fire. I'd also want to see for example body cam footage and form my own opinion on the alleged "waistband" motion vs. accept the word of the guy who clearly screwed up on interpreting it if it even existed in the first place.
More generally, any system in which an ordinary person can be shot for opening their front door is flawed on its face.
But I agree the officer likely did not start his day wanting to murder someone, did not commit murder in the sense that word is generally used, and that our system needs to understand that no one doing any demanding job is consistently perfect. That means being able to call a mistake a mistake without it being a murder charge (which is what leads to people being so defensive about obvious screw ups and therefore prevents the system from working on improving itself like it should.)