I don't think you can consider that an invention. or inventing.
I used the exact same thing(only smaller) with kingsnakes many years ago(30yrs). In fact, all my husbandry is derived from my snake husbandry, only hotter.
It basicly, a method to dulicate the way saxicolis reptiles thermoregulate. I copied piles of wood and tin, I use to snake hunt in.
I guess I successfully used them, then other people came over and thought that they were handy and used and abused them. So now its popular.
Many species of monitors cannot use them, as their structure will not allow them to flatten out. These species often scar up their backs. Those species need burrows or hollow logs. Thanks FR