Major and Minor are two of seven modes. The scale in this song uses an Ab in the key of G-minor, (that's imprecise, but the best way we can think of it). The flat-2 note in the III mode can be heard in traditional Catholic Church music (think Holy Modal Rounders); every week I actually sing this mode in the Lord Have Mercy (Kyrie Eleison in Greek), in Church called the Phrygian mode. The song composer, Flatbush Waltz, is mandolinist Andy Statman. The Quebe Sisters Texas Swing Band at the Library of Congress Andy Statman's FLATBUSH WALTZ https://www.youtube.com/watch?v=FN1mODxfd18&t=15m56s