That was my point: there are huge anachronisms (magic being by far the most obvious), so there's no need to pick on one aspect which, although it may seem less "realistic" to us, is probably one of the few things in the series which stands some chance of being true for the period**.You are taking this far too seriously. It clearly isn't any period in history in this reality. Not only that but have you ever seen those mountains in England? And when did you last see giant Hamsters? Or that French castle they all live in? As for the siege tunnels, by that look of that map the ground beneath them must resemble Swiss cheese!
** - The period being one when a warlord might have flourished and been successful without leaving much, if any, trace in recorded history.