That "stub" is Galicia. Roughly, Galicia is to Spain what Scotland is to Britain. It was independent until the time of Queen Isabel, and has regional autonomy today. It also has its own language, Galician, which is a kind of Celtic-inflected mix of Spanish and Portuguese, with its own Latin-derived twists.

One thing I didn't know and learned from the language map is that Galicia was invaded by the Swabians (or Suevi), a Germanic tribe that in turn was fleeing the Huns.