A long time ago, Michael Wagner received his first ukulele as an unwanted gift from his brother. Shortly thereafter, Michael went on a camping trip with another brother, and the ukulele was the perfect sized instrument for the trip, and provided Michael with hours and hours of time to explore this odd little instrument. From that trip came a joke song about Hobbits, sung in the style of Led Zepplin, but that's not the interesting part.
While Michael was playing around with the Zepplin spoof song, he accidentally hit the ukulele in a way that produced a distinct drum sound from the sound hole. Michael's OCD went into full-gear, and he went on to develop a completely new playing technique that redefined the ukulele as a hybrid percussion-stringed instrument.
The result is a playing style that tricks most first-time listeners into thinking that they're either hearing two separate performers or that the tracks are being over-dubbed. However it's just Michael and his ukulele.