It is included in the Archive as two recordings made in Inishowen in 1984 and 1990. I believe that is totally legitimate in an archive dedicated to the songs sung by traditional singers. The lyrics are credited to Stewart Ross, perhaps as a result of your contact with them.

If you hold copyright on the song, you can require that those recordings be removed, thereby erasing the fact that the song had currency in Ireland at that period. You can take legal action against them for damages sustained, which will incur legal expenses that you may not recover as the damage would appear to be minimal and the action disproportionate. You may be able to require as a condition for retention in the archive that it be labelled as a song of Scottish origin.

In all this, note that the tune (as distinct from the lyrics) is credited to others, including the accordianist Iain McLachlan, but that that attribution is also not certain.

Note also that anyone is as free as Stewart Ross was to compose other lyrics to this air, as others have done including apparently Mike Oldfield. Provided, of course, that those lyrics are sufficiently different from Ross's to constitute a new composition, and provided they comply with any extant copyright concerning the tune.