You are correct about the recommendation to cure black walnuts in a dry, cool place out of direct sunshine. However, I cannot find a reference why this is so. 

I believe, having cured walnuts before, that this is because you want the walnuts to slowly lose moisture content over the two-week period.

Curing prepares the walnuts for storage and allows the flavor to develop. When the nut is dry enough to store, its kernel will break crisply, with a sharp snap. If cured improperly, nuts will mold.

All the best, Roxanne