If you assume WotC verifiably knows exactly how he came by the cards before knocking on his door, that's the worst.
If you don't assume that, then there's the $4000 value of the possibly stolen goods, and the unknown value of other theft or loss through the supply chain implied by those cards being out in the wild that would be of concern.
The leaking of details, by the way, eats into WotC's ability to market the cards - reveals of the content of the cards is part of how they entice people to buy.