Was he from Tuva? The folks there do those sounds pretty regularly with only their mouths.
I did play jews harp for 40 years as a part of my performances and also used it on recordings every so often too. Songs like "Cotton Eyed Joe", "The Swap Song", "Father, Oh, Dear Father", "Turkey In The Straw", "The Kansas Cyclone" and a few others. I played it with a foreward sweep of my hand with a quick sweep backwards producing a staccato succession of notes sort of like a flatpicked guitar or an Earl Scruggs style banjo tune.