I know uchuvas do have a perpetual wet feeling, and I imagine the clammy ground cherry does too. Tomatillos (alos called Mexican husk tomatos) are also in this family (P. philadelphica and P.ixocarpa), and they're sticky too when you first peel off the husks---so I think this is a case where all (or anyway most?) fruits in this family are sticky/damp, and poor old clammy ground cherry just got stuck with the name. Or maybe it's more so than others!