Brendy: the Viking invasion of Orkney eliminated the Celtic population (at least, presumably, the male elements). My understanding is that only one place name with Celtic roots survived on Orkney. Considerably less than the number surviving even in Northern England. The language of Orkney remained Norse, the local variety known as Norn, until recent centuries, when it was replaced by Scots (or English) not Gaelic.

I don't doubt that travellers from the Highlands and Western Isles will have ensured that Gaelic language and music remained known on Orkney up to fairly modern times. But for a band from the Northern Islands, the Gaelic language is not "their" genuine "roots"/traditional source. However, that was only meant as a light-hearted aside, not to cast any aspersions against the music.