Their reaction was oddly appropriate, because their ignorance mirrors our own. Westeros feels "empty", like an empty gameboard where characters are moved to and fro at the whims of the screenwriters. For all intent and purpose, all of Westeros except Winterfell and King's Landing is completely bereft of people, a landscape of empty castles and cardboard cities.
This is why the constant talking about "gaining the support of the lords of Westeros" rings hollow. This is why two characters sitting in a inn can offer the Reach to a random cutthroat. This is why the throwaway mention of "the new prince of Dorne" feels weird.