Without a doubt, they would seek a supernatural explanation, because nothing else could possibly make sense at the time.
I'm still curious why ancient people people felt compelled to build pyramids. We see it in virtually every ancient culture from Egypt to Peru, and north.
Dr Robert Schoch, in his book,Voyages Of The Pyramid Builders, speculates that all the world's pyramid builders originated on the Sunda Shelf (Indonesia) that went underwater at the end of the Ice Age. They took the culture of pyramid building with them all over the world as they fled the flooding. Also, he said that if there was an Atlantis, that was probably it.