The fault does not need to lie with just one element. The driver was clearly not operating the vehicle competently. No one will reasonably dispute that. But I have to ask why, with all the smarts that a Tesla supposedly has, no safety feature noticed the prominent, easily-recognisable, large obstacles directly in the car's path? There is clearly a major fault in the autopilot and/or collision avoidance system, either in detection or decision-making, to allow this to happen.
Even if the driver is at fault, you can still blame the seatbelts that chose to disconnect and eject him out the windshield because it was a rainy day on a Wednesday, and sue the car/seatbelt manufacturer. I don't see why such a glaring fault in the automation here should be excused any more than a faulty seatbelt would.