This thing looks like it may have been built for a defined purpose but he doesn't state it in his ad.
Its that, or he just found some pieces and welded them together and said look… it floats.
I dunno, I think a couple of six packs of cheap beer and the sentences, "hey, someone is throwing away one of them bigass stainless barbecues, let's throw it in the back of the truck" and "holy shit, that is a shitload of restaurant ductwork! toss it in the back of the truck with the bbq!" played a significant part in both design and construction.