Well, obviously the number of autonomous vehicles involved in accidents is going to be lower, but that's because barely any of them exist compared to the vast majority of people driving their cars. If you had statistics on proportions though, that might be a different story.
You missed "per distance travelled" - that partially normalises the results. You still have to adjust for situation and road type (which Tesla conveniently doesn't do in their advertised numbers) for a better result.
