Sounds much like a balalaika, but tuned lower and with a bass string. Notably, a balalaika has just three strings, of which two are tuned to the same note. And requires constant black-metal tremolo picking due to short sustain.

somewhat similar technique from mississippi guitarist RL Burnside. brush downstroke with the index finger, and upstroke, with the thumb downstroke. But Burnside anchors his hand below the neck while Kachamba has a freer strumming motion.

Shame there isn't a lot of recorded music from him to listen to. Thanks for posting.