The word rún was present in Old Irish, so it must have been in use no later than 850. Waterford was the earliest Viking settlement in Ireland, founded in 914, so it seems as though the Old Norse word rún was independent of the Old Irish word rún. (The latter could also mean “mystery”, which doesn’t seem to be the case with the former.)
Since na Rún is genitive, the Wikipedia contributor should have put a leading “The” on each of the possible English translations.
Another possible (but unlikely) translation of Ros is “Flaxseed”. Dinneen also offers “a plain, level tract of arable land” as another meaning of the “headland” Ros.