It's all about "regulatory requirements, governmental oversight, HUD standards and local government rules/laws"....
HUD defines a "manufactured home" as larger than 400 square feet of living space.
The RV industry defines a "park model" or an "RV" as "no larger than 400 square feet" and since it's not a "manufactured home" it doesn't have to meet the minimum HUD requirements for energy, insulation, building standards or "minimum structure requirements"... Think about the hurricane building codes for "manufactured homes" in Florida.... They don't apply to "park models" which are "classified as mobile" so they can be "moved out of harm's way"..... At least that's what "they claim"....
It's pretty much a "shell game" to build products without government requirements and to skirt the requirements established for "full time living" and a way to get around the local building codes by calling them "recreational homes".....
Here's one of hundreds of articles about the differences and similarities:
https://www.howtolookatahouse.com/Bl...standards.html