Thainin (first post) and Thaining (second post) should be "Thàinig" -past tense of the verb to come, "Thàinig mi," I came.

(Capercaillie is the spelling of the band's name, and of the bird; diffent is different and coection is collection)

Usually if you get the same vocables in the chorus, the song/s will have the same tune. Some readers may need to be told that Mouth Music is the name of an album featuring Talitha Mackenzie; the Hoireann O song doesn't belong to the Port à Beul (mouth music sung for dancing) category. I would guess it is a song for waulking the tweed, but it has been given a modern treatment in Talitha Mackenzie's and Capercaillie's renditions.

Celtic Lyrics corner gives a translation of the Capercaillie lyrics
http://www.celticlyricscorner.net/capercaillie/hoireann.htm