Dunno exactly but im pretty sure cornwall used to be a part of Wales? Maybe someone better versed in Britain history could clear things up.
As far as I know, linguistically both regions spoke Common Brittonic at the time Seibah would have been alive, and Cornish and Welsh are both descendant languages of Common Brittonic that diverged after the Angles and Saxons took over and cut the surviving islands of Brittonic/pre-Anglo-Saxon culture off from one another.
Its just that "angry Common Brittonic" noises is a gag only linguistics nerds would get, and if you're updating to the contemporary descendant language for recognizability then Cornish is the more accurate region to correct to.
