What about the accident rate per miles driven? If that is dropping too I'd see that as confirmation that it really is improving. If that isn't then it's just bookkeeping.
You can read all California autonomous vehicle accident reports here.[1]
Most Waymo reports are "stopped in traffic, was rear-ended". There are two reports this year where the Waymo vehicle was responsible. In both cases, it was backing up while doing a three-point turn in a narrow street and bumped into something at 2MPH. So they need better sensor coverage in back.
