I just tested creating several games on the Arborea map type. For the tests, I created games with Pangaea, Islands and Large Continents as the landmass type. All three only show that it's the Arborea map script, but not which landmass type was selected. The icon of the map script is always the same icon as the normal continents map. In these tests it seemed more likely to get a coastal start on all but Pangaea. However, some Pangaea games did get coastal starts. Even on Large Continents I've seen starts that were far enough from the coast to not see any water. I've also seen starts on Large Continents that looked the same as the Islands start.