Although the planet clearly has more advanced technology, David’s society is agrarian.  They are mostly rural farmers and still use animals for travel.

David’s dream at the beginning of the book describes a world much like our own, but it is foreign and strange to him.

And the buildings were quite unlike any I knew. The traffic in the streets was strange, carts running with no horses to pull them; and sometimes there were things in the sky, shiny fish-shaped things that certainly were not birds. (ch 1)

Contrast this with the level of technology David's people have.

I had made my way down the cart-track to the south, along the borders of several fields until I came to the high bank, and then along the top of the bank for quite a way. (ch 1)

David’s grandfather arrived with a wagon train, and the people never advanced past that point.  This makes sense because the people are suspicious of anything different.  Of course they will never grow and change.  As a result, David’s world resembles 19th century America, even though it would seem to be many years in the future.  The blast to the past was a direct result of the apocalypse.