I've been driving 17 years and have had two fender benders, one was my fault (within my first 100 hours of driving, I got a lot more cautious after that), the other was rear ended on an entrance ramp that often backs up, and the person behind me wasn't paying attention (I was at a dead stop in traffic and they hit me).
I'm not saying I'm a stellar driver, but I think I'm average, if these cars are driving a lot, the numbers seem reasonable (I drive 15-20 thousand miles a year, I've had one not my fault accident in 17 years, and one that was mine).
What we don't know is the criteria for switching to Human control, the two autonomous accidents may have been easily avoidable, and all non-easy driving may have been under human control. Lack of data makes speculation almost useless.