those things- he went to the apartment reported. He did the right thing by announcing himself at the door twice. It appears that it was the wrong apartment for the DD but he didn't and couldn't know that. He properly and loudly announced his presence. He did not cover the peep hole. The Airman answered the door holding a gun. The question is, did the deputy act as a reasonable police offer would act given the totality of the circumstances.

This can be a horrible tragedy and the officer can acted completely reasonably given the circumstances.

So I'll ask again, what exactly did the officer do wrong given the information presented to him and based on what we witness in the video?

The only place I can see any room for argument is that the victim did not appear to raise his weapon. But given the prior information of the loudly announced presence and the fact that the officer reasonably believed he was responding to an out of control domestic disturbance, I don't see how you can arrive at the conclusion that he was unreasonable in his actions, let alone "out of control"