Someone who got the "diary picture" from the owner of the picture ( = owner of the coins, who also made the picture says the FAQ) and asked the organizer of the challenge to get the WIF as they have not the knowledge to compute the remaining part.
...which actually belong to @soferox
How do you know, that soferox is the owner?
Well for starters, he wrote that his notebook with Bitcoin private key was damaged by a flood, and since I never saw him talk about any challenge like this, I'd say it's not likely for him to be the challenge organizer (unless he explicitly mentioned that in some post that has eluded my attention).