Very interesting concept/design, not seen anything like this before.
My first thought was about the hinge pin then I scrolled down and saw the example has what looks to be a peined over metal pin, so that could be done with a small brass or copper nail or sturdy wire.
It will need a projection from the handle to locate on the bowl ( or a square joint edge) to stop it dropping, not sure if this is feasible from a one piece carving or if in fact the two parts were carved separately from the one stick.
Very interested in how you resolve this and other people's ideas/comments too.
Super project to do,
Rob.