Reportedly, the driver of the car below honked at the pale SUV in the road just ahead because it was moving slowly on the road.
The passenger in that SUV evidently had a great deal of feelings about that interaction, as is shown in the camera footage below. He stormed out into the rain and leaped with a full body slam onto the driver's hood and began wrestling and shouting with the windshield wiper. After he gets off the hood, it looks as though the driver's windshield is cracked.
Unfortunately, the video clip begins after the honk supposedly happened, and therefore doesn't prove that a honk is what actually triggered this confrontation.
Regardless, there are very few scenarios in which case that display of hostility is understandable. Yikes.
Here's a version of the video with sound:
If you listen closely to the audio, you can hear someone over a phone saying, "Get away from him," and "tell me where you're at."
It's likely that this is either a parental figure or a 911 operator on the phone. That suggests that the interaction with this road rager had been going on for long enough that the girls called someone about it, perhaps even that the SUV had been following and aggressing upon them for a little while. However, please keep in mind that hypothesis is purely speculation.