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:
Adobe Premiere is affordable software to manipulate videos.
Occam's razor? The simple assumption is, "this is a faked video." It's not the unbelievable assumption that this person's hand is unique in human physiology- every finger, and finger joint is double jointed, and, he has the muscles to actually pull his thumb and fingers backwards.
One double joint, maybe, but 14 or more, one one hand? NO WAY.
This person would probably be on the news, if he could grip backwards. He'd be of great interest to scientists around the world. I say, don't believe everything you see on the internet. If it looks unbelievable, it's probably fake.
Glad you responded. I'd love to delve deeper into this.
First off, no one is suggesting he (seems like a male hand) can grip backward. He never picks up the bottle. He can only bend his fingers back far enough to to make it look like he can grip the bottle. I doubt he can bend far enough back to actually pick it up.
Secondly, saying that Adobe Premiere is affordable and can edit videos is akin to claiming that a pick axe is pretty cheap and can cut marble, therefore I could use it to make this:

Adobe Premiere is used to edit videos (and a couple cheap special effects like 80s lightning). And when I say edit, I mean arrange shots in different orders. It does not have the ability to morph two videos together. That's the realm of much more expensive programs.
Plus, to do that it would have to be done on a green screen so that the background isn't morphed as well in the process. Then the background would have to be added in later.
However, the hand is at the same time passing in front and behind the water bottle, and yet the water bottle is never morphed. It was obviously not done on a green screen, and yet the bottle remain perfect except when the hand itself moves them.
You could say "Well they probably just did it twice and hid the cut real well when the hand moves". Ehhhh maybe, if the camera was still. But the camera is not still, it's moving around. And the bottles still remain perfectly still, and there's no detectable cut point (ignoring whatever it is that Darth thinks he sees). Any sort of video editing is made even more difficult when the camera is moving, and that movement is not done in post as everything is changes sizes in relation to the movement.
Also, if it was two videos with two different hands, he went to extra lengths to make it look like it was a hand that was bent backward, as the thumb looks messed up when it's on the left, and the motion is real creepy.
Now, while this could have been done by a professional with some serious video effects skills, you have to ask yourself "why?". Why would they choose to do that and then go through all the really hard work to make it look like a crappy cellphone video?
And here's where I think Occam's Razor is the strongest, and it has to do with creativity. It's really hard to be creative, and to think up something new. Not only would this guy have to go through all the time consuming and skill intensive work of creating a video that looks home-made, but he would have to have the original thought "Hey, it would look really freaky if I made it look like I was grabbing a bottle, but really my hand was bent backward." He would have to have that original thought, and then also happen to have the skills to execute it.
Now which is simpler: what I just explained, or some kid saying "Hey look what I can do!" and then uploading it to the internet?