No worries, and you are indeed correct. Let me amend my post.
Then again, common hexadecimal notation is alphanumeric when seen from a base-10 perspective (as I'd guess most people do). Of course, this entire post is just a base-128 number, and contains no letters whatsoever.
...and the words only made it onto the forum due to quantum entanglement between the keyboard and your computer. :P
Could this possibly be one of the keys that was distributed as part of one of the nVidia video card promotions?
Quite possible, though I was under the impression the promotion was until the end of May 2015. Unsure if that is how long you can redeem the code in nvidia's site or when the GOG codes expire.
While the ability to get a code for a qualifying purchase may end in May, I'm sure there is a grace period one is allowed before its actual redemption.
I just recently purchased an nVidia card, so I'm supposed to get two games codes within 7 days of my purchase --I haven't received them yet, but according to Amazon, I will. The Witcher 3 code has already been slated to be given to a friend, as I had pre-ordered the game many *months* ago.
BTW, the OP was very smart on blotting out the code with the picture they posted. Otherwise, it would have been redeemed well before its date of expiration! :)