Highlanders are distinctly Ala Mhigan in origin, though lorebook suggests there are Highlanders who have been part of Ul'dah long before the fall of Gyr Abania. There is also a Highlander in the MSQ who states he is from Othard.
There's also the idea that just because a character has a Midlander or Highlander model, that they are not necessarily of that clan (though still a Hyur or whatever). Minfilia and Yda are Highlanders. So you could play a character with the Highlander model and not necessarily BE a Highlander. The Ninja NPCs are of the 'Far Eastern' Hyur clan, and are not Midlanders, for example.
There's also the idea that just because a character has a Midlander or Highlander model, that they are not necessarily of that clan (though still a Hyur or whatever). Minfilia and Yda are Highlanders. So you could play a character with the Highlander model and not necessarily BE a Highlander. The Ninja NPCs are of the 'Far Eastern' Hyur clan, and are not Midlanders, for example.