Most drivers aren't pilots. They don't know what autopilot actually does. They expect it to drive the car for them, and they probably think autopilot does the same on planes. It was a mistake for Tesla to borrow the term.
IIHS did a survey of 2000 people and a driver assistance system named "Autopilot" received the most responses that overestimated the system's capabilities. For example, "Nearly half — 48% — thought it would be safe to take hands off the steering wheel when using the system." In general, about 50% more people overestimated the capabilities of Autopilot compared to the names used by industry leaders (ex. SuperCruise, ProPilot Assist). Other things users were more likely to think they could do with "AutoPilot" included texting and watching a video.