Adding another room to your camper...

I would say it was done out of necessity. If the camper were sitting directly on the flatbed it wouldn't clear the cab, nor would the drop in the back clear the flatbed either if it was forward against the cab. My guess would be they have some sort of hatch/door in the camper interior to get into the added space like on some boats.

You do what ya gotta do sometimes. Build a riser for it like they did, buy a new smaller flatbed and raise it somehow, buy a new camper, buy a new truck your choice, your money