Deep Gnome Stone Camo, does it only applies in difficult terrain?

@JeremyECrawford Deep Gnome Stone Camo, does it only applies in difficult terrain, or applied in areas that are rocky ie: caves, mountains?

— Matthew Harrison (@MattyH82) April 10, 2016

Stone Camouflage works in rocky terrain. The terrain needn't be difficult; the trait would say if had to be. #DnD https://t.co/U7PTZCtBYH

— Jeremy Crawford (@JeremyECrawford) April 12, 2016

@MattyH82 I'd apply it in any stony environment

— Mike Mearls (@mikemearls) April 12, 2016