The officer attempted to stop the perp with non lethal shots, right hand and arm focus. Didn’t work. Someone keeps charging you go for the kill shot. Brown’s size pretty much guaranteed it would be officer down had he reached Wilson.
I highly doubt that. I know of no agency or academy or even a private training institute that trains that way.
Most likely scenario is how he mechanically pulled the trigger or where his vision was focused under the stress of the incident.
The “non-lethal” shot stuff is really bad television writing.