How did the backrooms even become what it looks like?

When Async opened the "portal" to the backrooms, it looked like the normal backrooms. The inside of some crusty old grammas house. But, how'd the backrooms know what the interior of a building would look like? Wall trim, ceiling tiles, even the carpet and wallpaper.

How did the backrooms take inspiration or have knowledge of our reality IF it never had a connection to us before Async?

And if there is another life in our solar system, why would the backrooms only take from our planet?

(btw idk if this has been debunked or not lol)