After enlarging and poking at the photo as much as I can, and spending a couple of hours looking at pictures of High Country tailgate accessories, I think it might be just that funky multi-flex tailgate Chevy added a couple of years ago. When it's folded a certain way, it has that rolled-up look.
But it still looks like there's some kind of extra attachment near the back of the box. I found an almost infinite variety of custom and add-on tailgate designs, things that fold down to tables or open in thirds to accommodate loads, or allow a tank to be loaded in a box with only a small hatch to access the spigot, etc. etc. etc. etc. etc.