Continuity mistake: When Nan first swerves to avoid The Hitch-Hiker, her 1959 Mercury briefly turns into a 1957 Ford. It also changes from a light to a dark color. (00:17:15)
Continuity mistake: After Nan sees Hitch-Hiker for first time and she starts speeding away, she has clear road both in front and behind her. But just seconds ago, a mechanic told her to follow him to his shop so he could change her tire. Where did he go?
Factual error: The Southern Pacific train that almost hits Nan's car did not serve the part of the US she was supposed to be in.
Answer: It's explained in the episode. The aliens are experimenting to see how humans react to various scenarios. This just happens to involve them using super strength.
Thanks. It's been a long time since I saw the episode so I forgot.