You're both right! Cell mobility is enhanced in wet / moist environments, as are the ion gradients that help guide cells to wounds. So during the initial phase of healing keeping the wound moist promotes healing, however it will never "close up" except in dry conditions. The promotion of the formation of scar tissue and other outer layers of skin is triggered by air + dry conditions. (When you get skin cancer you learn all sorts of fun things, wear your sunscreen kids.)