Just one of many of life's unanswered questions
You’re correct- it was whatever they left behind before departing the moon to head back to earth. Was that the LEM?
Anyways, I have read that the one from Apollo 11 is still in orbit.
The next ones they crashed ito the surface to record their impacts in the instruments they left on the moon (to detect moonquakes).
I also read that the moon ‘rang’ for 3 hours afterwards, suggesting it is hollow.
So it is probably filled with aliens who watch us through little peep holes.
Just one of many of life's unanswered questions