Not that I think jumping on the top of someone's car is obviously justified, but I am honestly curious how the car got to this point. Wouldn't it have had to drive past hundreds of people into what was obviously a large gathering to get here?
Besides the car being a Waymo (which may or may not be part of the reason why it was "swarmed"), it must not have been such a great experience for the driver to be circled and have people jumping on the car bonnet and roof, I guess it could have happened to any car happening to pass by that intersection.
And all cars were eventually let through after some heckling / jumping.