Well, the name preceded the environmental changes wrought by the Calamity - Sixth Astral Era Thanalan was a dry, desolate wasteland with only occasional patches of vegetation and even less permanent sources of water. Ironically it's considerably more greener now than it was 'five years ago'. Incidentally 'Drybone' refers to the small muddy pond in the centre of the zone, which the settlement takes it's name from. But yes, there is now a surprisingly high amount of rainfall now falling there, which does make it seem odd.