As a Mandolin and Whistle player , if I play , for example ,'Old Joe Clark' does it cease to be a Fiddle tune ? I dont think so , any more than 'The Barren Rocks of Aden' ceases to be a Bagpipe tune when played on a 5 string banjo !
Gypsy , I think your Mandolin player is being just a touch precious about his music (In My Not Very Humble Opinion).