The third vehicle (pickup truck) decided to go around instead of stopping, probably because of the vehicle behind that was driving too close. That caused a larger pileup than it would have been if the fourth car maintained a safe distance and speed.

This is partially the fault of Tesla, but it could have just been any other car having issues such as running out of gas, or an engine failure, or a medical condition with the driver… and the result would have been the same. That being said, there’s obviously no reason for FSD to stop the car like that - Tesla needs to figure out these random stops in the middle of a freeway