It's not unreasonable for people to think that "autopilot" means something that automatically pilots a vehicle. According to a dictionary automatic means "having the capability of starting, operating, moving, etc., independently". Whether or not that's how actual autopilots in airplanes and ships works is irrelevant, most people aren't pilots or captains. Tesla knew what they were doing when they chose "autopilot" instead of "lane assist" or similar, like their competitors did. It sounds more advanced that way, in line with how their CEO have been promising full autonomous driving "next year" for a decade now.

It's also worth noting that the recent ship collision in the north sea is thought to be because the autopilot was left on without proper human oversight, so even trained professionals in high stakes environments make that mistake.