In this case, there was still residual moisture in the nettles. The plant consists of parts of different thicknesses (stems, large leaves, small leaves). Each leaf also consists of parts of different thicknesses. So if one part of the leaf is already rustling dry, the thicker part of the plant may still contain moisture. Moisture may also be released during cooling.
The ambient humidity also influences the dryness of the dried food, as it draws moisture from the air (‘hygroscopic effect’).