When a person is armed, in a vehicle, and is observing someone that is suspicious, and the situation deteriorates to the armed observer, lying on his back and getting beaten by the lone suspicious person, one thing is clear:
There were tactical and probably strategic mistakes made by the armed observer. Without a doubt.
Any number of things done differently by either party, would have changed the outcome to not being fatal or even violent. However, tactical or strategic mistakes made by either party, is not sufficient, by itself to make them deserving of injury or death. The legal question of responsibility for the actions / guilt of breaking the law, requires quite a few facts, before it can be answered beyond reasonable doubt.
At this point, some of the "facts" I am aware of appear contradictory. What actually happened is not clear to me at all.