Explain how an internal prototype from "a year and a half ago" would be seen by
anyone outside of Nintendo's R&D and upper management, let alone someone with enough access to take a photo of it, let alone someone willing to face extraordinarily severe repercussions? Especially when developers weren't anywhere near getting NX dev kits that long ago?
Furthermore, again, as has been said Nintendo doesn't file full design patents before a reveal. Additionally, the patent that that this "leak" matches is simply a filing for the application of touch screen free-form displays on game console controllers,
not a general design patent. Concept application patents almost
never use real designs, for (hopefully) obvious reasons. Those patents are filed before the products that implement them (if they ever even exist) are revealed, to protect any possible ideas the company comes up with. They're not going to attach actual designs to them because 1) they have literally no reason to, and 2) they'd be giving away major details of their product before it's even revealed. That's why the general design patents (like the GamePad patent image floating around in this topic) are filed
after reveals, so that they are able to reveal the final product design on their own terms.
By the way, here's another completely different NX controller patent, this one for the scroll wheel triggers: