I was shocked when I watched this, it's like Wolves running down an Elk or something. If you watch the start again, knowing what comes afterwards, it's clear that the bikers already have some beef with the Range Rover driver. Something, however trivial, prompted the looks across, crowding and then eventually the idiotic brake-test thing.
I don't blame the driver for doing what they did, the "gang" were asking for that, it's fight or flight. I would have made sure that the next time I stop the car is at a police station, though.