That particular form of words is found only in the set published by Ewan MacColl. I don't have a copy of his Scotland Sings, but it's possible that there is some explanation given there. Bronson (III, 164) prints the MacColl tune with the comment 'Latterly, Ewan MacColl has recorded the ballad with a tune learned from his father and a text from Child's B, or Finlay [Scottish Historical and Romantic Ballads, 1808].'

MacColl frequently expanded fragments learned from his father from print sources, and that is the case here. 'Learned from the singer's father in a fragmentary form and collated with verses from Child's texts' (sleeve notes, The English and Scottish Popular Ballads, IV, Riverside RLP 12-628 (A1)). Most of the text is as quoted by Child from Finlay, but compare the final verse from Child/Finlay:

Crawing, crawing,
For my crowse crawing,
I lost the best feather i my wing
For my crowse crawing.

Whether MacColl's form of it was just as his father sang it or whether it was his own re-write, I wouldn't know. It's possible that he made some further comment on the subject elsewhere. The word is certainly 'tint' (lost), though.