We don’t need to guess here, Waymo is way safer than human drivers as a car and a pedestrian. So clearly optimizing for “not confusing human drivers” is not correct.
Human drivers frequently run into stationary objects and plow over bikers/pedestrians so maybe there’s a huge category of situations where they *should* be surprised
That's why I said "one of the most important", not "the most important". Driving in the least surprising way is one of the methods of avoiding accidents.
If Waymo's driving style means that they get rear-ended more than normal, that means that Waymo is behaving in a way that surprises other drivers. While it's true that the fault is the driver that did the rear-ending, it can also be true that the accident may have been avoided if Waymo drove in a manner that didn't surprise the tailgater.