Isn't airplane autopilot only used when there's no traffic around. An analogous autopilot for cars would never be used unless if you're in an empty parking lot.
Yes, anybody who has used an autopilot on a boat or airplane will understand that they work exactly the same way the "autopilot" on a Tesla works. But that's not how the general public understand the word and so Tesla shouldn't have used it in advertising copy aimed at the general public.