Looks like an art project to me - not necessarily yours (or did YOU organise this for the photo only :shock: ????), but you sure profited from it by this rare chance to take their photo.
I've seen reports on this artist, now what's his name????, on various culture programmes on TV recently, he always goes round to ask people if they - many of them usually - would want to pose for his photos in the nude, and many agree! Was it him around somewhere, maybe?