Nope. I can reproduce that same odd-looking position with my own right thumb. The optical effect is just that the thumbnail and tip of her (and my) thumb is at a fixed angle upward, and bending the next thumb joint downward puts the overall thumb into a sort of 'Z' curve. Hers is a little more pronounced than mine, but it's the same idea. Try it -- I can't guarantee that your thumb is shaped like hers or mine, but trust me, it's not bent backwards, it just looks that way.
With my arthritic hands, I couldn't bend it if I used pliers...LOL!