The ngoni, like the ukulele and the 5-string banjo, are examples of instruments that use re-entrant tuning. This term is used to describe the use of tuning that has the highest string before the lowest string, unlike a guitar lute or fiddle etc where you get to the lowest string first.The ngoni family of instruments, as far as I know, don't have the short high string, and neither do early American banjoes; that was a refinement added later by an American called Joel Sweeney, or so some say, though maybe he just popularised it. The history is extremely murky, as are most folk-related topics!