Continuity mistake: When Roy leans towards the steering wheel to watch the UFO, the position of his hands over the wheel changes between shots.
Continuity mistake: The mashed potato that Roy serves himself swaps from stiff to creamy between one shot and the other.
Answer: It wasn't definitively answered, but it appears the aliens took people in order to learn more about humans. It's unclear if all those who were returned had originally gone willingly, but the intent was not to keep them indefinitely or harm them, and they were returned to Earth, albeit many decades later. At the end, after the aliens had made contact, a new group of humans, including Roy, went with them voluntarily.
raywest ★