I am amused that people think only here and now has ever had advanced technology.
Archeology has found many enigmas where a culture that lacked any other form of advanced technology possessed many practices that defy explanation.
The druids building Stonehenge with such mathematical and astronomical precision that even how much the stones would sink into the ground from their weight was accounted for...but they lived as druids.
A culture that deals with their dead by setting off the corpse in a hot air balloon...but lacks any understanding of the concept of flight.
Remnants of what appears to be a spark plug...primitive, but built to the same design of a modern spark plug.
Any number of catastrophes could have taken an advanced society and forced them back to a barbarian stage of existence. Why do we presume that ancient cultures didn't possess more knowledge and understanding of the sciences than we currently do? Just because of how they live today?
First of all stonehenge was never associated with the druids until the modern era, second I would hardly consider moving some boulders an enigma - hack away in a quarry until you have a big block, grab a couple dozen men, beasts of burden etc, put some kind of roller under large block, pull, pull some more, more pulling, keep pulling, eventually get there, use basic knowledge of force to pull stone upright. Astronomical precision? People celebrated the solstaces because they marked the changing of the seasons, important dates if you rely completely on subsistence farming, I'm sure yo can image someone figuring out a way to mark that date by placing stones on the ground that match the sun, hell I remember marking shadows on the ground with chalk when I was 4.
Someone builds tent out of light materials. Someone puts tent over fire. You can see where this is going, I've never even heard of this before and I can come up with an explanation.
I'm highly dubious that it was identical to a spark plug, but I'm certainly aware that "batteries" (it's never been shown that they were actually
used for anything) taking advantage of electrolysis exist, but does that mean sticking a couple of wires into a lemon is something that requires advance thought? It's not hard to see where discoveries that apparently mimic modern inventions come from.