Dr Robert Schoch wrote a book,
Voyages Of The Pyramid Builders, with the same (out of Sundaland) theme. He said the Sundaland refugees took their custom of pyramid building with them all over the world.
We still put out our seit stones, of course. Always wondered why we did that, then they invented the internet!
BTW, many of the "mounds" found in Midwestern river valleys have more than one purpose ~ they become places to move out of the flood waters in Spring.