And then I had a piece of it. It turned out to be compressed watermelon, infused lightly with pickled ginger. Compressing the ginger expels some of the water (flavourless) and then any flavourings are reabsorbed. Clever stuff.
So on the phone to Chef Gilbert - "is this doable at home?" using a regular vacuum "FoodSaver" rig. His simple answer - "yes, go for it".