Yes, you have the right questions backed by facts.
Finnicum was not a danger to them or anyone. He was defiant. He was told to get out of his car and he did. But he was defiant saying he was going to a meeting with the Sheriff and there was nothing illegal about that, and that if they were going to shoot him, then go ahead and shoot him. That conversation is all recorded.
So he knew they were there to kill him. For what? They wanted to kill him as a revenge on the Bundy standoff in Nevada. This was McCabe carrying out a revenge killing for Hillary and Reid.
Like he carried out his revenge on General Michael Flynn.
I'm still not certain that he didn't get out because shots were hitting the vehicle in order to draw fire away.