Why did he have a gun?

Demonstrably, to protect himself from an attacker.

You don’t take a gun with you unless you’re ready to use it.

And he demonstrated that he was ready to use it to protect himself. What’s your point?

You don’t use a gun unless you’re ready to kill whatever you are pointing it at.

He didn’t point it at or use it on anyone except those who were literally in the act of trying to kill him.

What’s your point, exactly?