It most probably was the GM demo item and it makes perfect sense for it to be there if the purpose was to show it to invited guests. In my day at Fairford, the RIAT Reception / Dinner was held in that hangar with car parking on the concrete in front of where the Global Hawk is - various back-drop items were in the vicinity (eg BBMF aircraft) and it would not surprise me if some exhibit opportunities were monetized. Just a guess.