I previously posted that "both drivers acted improperly."
Even though the guy in the trailing car seems to have been the aggressor (based upon the limited information that we have), the guy in the lead car could have handled it better if he was legitimately trying to de-escalate the situation.
The first thing he probably should have done was take a right turn onto another street to see if the guy in the car behind him continued to follow. If he took a couple of right turns in a row and was still being followed, that's a pretty good sign that he's being targeted for some reason (not necessarily for just driving too slow for the guy behind him). At that point, it's time to go into Condition Orange and look for other ways to take evasive action.
In a more common road rage situation, when someone pulls off the road into a parking lot, that can easily be taken as a challenge... as in "let's pull over and fight." If the guy in the lead car wanted to avoid a fight, he would have been better off putting on his turn signal and slowing down while pulling off toward the right side of the street and also waiving the guy to go around him with his left hand out the window.
He should not have left the street, which made it harder to speed away if necessary, and he should not have stopped his car while he was being followed, unless it was a police station parking lot.