Pure Malt whisky was often used to mean vatted malt, but I don't think it ever actually had a legal definition. Going back a few decades the term was often used on single malts as well. Dunglass is the name of a very rare experimental peated single malt whisky produced at the now-demolished Littlemill distillery in the late 1960s, at which time they were indeed owned by Barton. If your miniature is indeed of Dunglass single malt (and it looks a lot like it is), and if you still have it, hang on to it and for God's sake don't open it - it is extremely valuable.