This stat is widely misunderstood. Tesla rolled out Collision Avoidance Assist and Autopilot around the same time. These variables were not isolated by the NHTSA.[1] It is likely that collision avoidance was the major factor in the crash rate reduction. It is even possible that autopilot increased the accident rate.

No doubt collision avoidance is a fantastic feature though.

Addendum: Looks likes the NHTSA has disavowed Tesla’s interpretation of that study. They did not evaluate whether autosteer (autopilot) was engaged.[1]

[1] https://www.cnbc.com/2018/05/02/effectiveness-of-tesla-autop...