If you are on/in your property and/or feel you are in imminent danger of losing your life or suffering permanent disability, and you aren't the aggressor, yes...
Rightfully so, I say.
A single punch wouldn't make me feel I was in imminent danger of losing my life or suffering permanent disability... So no, if someone simply punches you I wouldn't think deadly force was necessary.
If they continue to punch you even after you have made a reasonable attempt to retreat, or (as in this case) if they stalk you to where you are going, exit their vehicle, approach your vehicle, and throw a punch at you when you are in a vulnerable position, then the grey area exists for our justice system to interpret.
The dude who was the aggressor was totally in the wrong in this situation. Not once, but twice.
I have value for people's lives. But why should I stand down to someone who doesn't have value for mine?