green granite. That was my first thought too. I suspect that the new kit is a bit smarter than your average Jindivik. Presumably, they need some reasonably flat scenery to fly over which would preclude a big chunk of Snowdonia.
I think the salient point is that these are test flights. It would seem advisable, then, to have some separation from a Robot that's still being programmed.
Whenever I see Wales and drone in the same sentence, I always think of Ieuan Wyn Jones!