Who knows what you did, if anything? Maybe you accidentally cut him off. Maybe he was going fast and got mad because he had to slow down when he ran up on you, which is stupid but some people are like that. You tried to make amends but he was past all that and just wanted to rage, but that's on him, not you.
As far as defensive driving, your best weapon is maneuverability. You can go between cars or quickly exit the highway when he isn't expecting it. I don't think a firearm is of much use, unless he forces you off the road and tries to attack you, but if it comes down to something as nasty as having to brandish a weapon or worse, shoot someone, you're looking at having to prove to a Grand Jury that you weren't part of the problem, which is very hard and expensive to do in a road rage case, even if you have video.
I'm actually experienced at Escape and Evasion (on foot and otherwise). I've run from weirdos, drug dealers, angry exes and even the cops at some point. If you have to run, have a plan. Choose a way that is easy for you and difficult for them. Choose a way that puts cover and concealment in your favor. Most importantly, never run FROM something. Always run TO something (as in somewhere more safe/defensible). And don't stop and look behind you.
This strategy is also beneficial if you do have to use violence to defend yourself. You can say, "Look, I ran for 15 miles, down side streets, between cars, rode up a staircase and all the way to this place and the fucker just kept after me. At that point, I had nowhere to run, I was cornered and I had no choice." Looks better than, "I pulled over, He pulled over, we had a fight and I killed him" Which could be anything from Manslaughter up to Murder 2 depending upon the jury.