Tesla actually use the correct term for it, the fundamental problem is a mass misunderstanding of what aircraft autopilot does.
Autopilot in an airliner is capable of flying the plane on a set course in ideal conditions. This means good weather, no other air traffic in the vicinity and full feedback from its various sensors. As soon as the plane enters a scenario outside of which it's designed to operate, control is reverted to the human pilots.
That's exactly how Tesla's system is designed. So long as the computers can account for the current scenario, the car drives itself, but it explicitly falls back on the human (who, like a pilot, must be ready to take command at any time).
A trucker pulling out on a driver and blind-siding them falls outside the definition of 'ideal condition' in my book. I live in Europe where underrun guards are mandatory on all trailers. Sounds like one wasn't fitted here. That's likely more to blame for the fatality than Tesla's software or a distracted driver - let's face it, anyone could suffer a lapse in concentration at a critical moment on the road.