A Passage for Trumpet - S1-E32
Trivia: In an era with no CGI, Twilight Zone used an inventive ruse to keep Joey from reflecting in the movie theater's mirrored wall. The "mirror" was clear glass, with a reverse duplicate of the set built on the other side. To "replicate" the girl in the ticket booth, they hired identical twins. (00:10:45)
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.