From their lp The Old Woman's Dance. Song from the Robert Tannahill catalogue wherein spring is welcomed after a severe winter. The tune was first collected in Niel Gow's Fourth Collection (1800) under the title Lord Balgonie's Delight (a very old Highland tune). Robert Tannahill also wrote the melody of Waltzing Matilda without knowing it. (see there)
It has been a common practice throughout the whole romantic history that classical composers drew inspiration from plain folk music. So why not mentioning it instead of signing bluntly under Michael's own name.