I saw the video from the helmet cam of one of the riders. The guy he "hit" on the highway got in front of him and deliberately backed into his car. You can see him even carefully looking back as he slowed. Then when the guy stopped his SUV they started slashing his tires in "retaliation".
I don't think this guy was unreasonable in thinking he was in danger and getting the heck out of there. I can see why he may have panicked.
Now this escalated everything.
The biker guy could have been "freaked out" but I believe that they deliberately targeted that guy after watching the video from the helmet cam. I could see no reason why the guy would carefully slow down to tap the guy's front bumper, and no clear reason for the originating attack on the vehicle. It freaked him out that somebody was willing to drive over the guy who stopped in front to block his escape... Maybe he'll think twice again before they target another person like that.