For good reason, I'm sure that the police officer was watching that driver-less car closely, and I can picture him following it for some time, waiting for it to make a mistake. At this stage in development, I think all driver-less cars should be treated as if they are a naive 16-year-old with a fresh license. 

Do driver-less cars see all pedestrians as an equal risk? For example, if a driver-less car were to pass a group of kids on bicycles, is it smart enough to anticipate the higher probability that this particular demographic of pedestrian can drift or suddenly dart into the street, and will it thus make a minor a adjustment to speed and distance accordingly? A conscientious human driver will make this type of subjective risk mitigation dozens of times while on their daily commute.