Yeah it's not photoshop. You'd need some pretty robust and expensive blending software to accomplish that. Occam's razor would suggest it's just a very flexible person, especially when considering this larger picture:

Yes, that is clearly the palm of a hand showing, as there are no 'life lines' etc. on the back of the hand, nor are there thick pads at the base of the back of the hand near the wrist (e.g. extending from the base of the thumb and on the pad on the 'outside' near the wrist). Also that is very clearly the inside of the wrist, as the tendons do not stick out like that on the back of the hand. [Plus the person is unlikely to have completely removed the hair from the back of their hand.]
I agree that the person's fingertips being hidden behind the bottle clinch the illusion.