i am guessing here, but in the Amazon, they probably used a hard wood- that could burnish up quite nicely. being a rain forest i dont know how they stopped the water from raising fibers- maybe a wax finish too.
i had Daniel Mannix's book "a sporting chance" as a kid- awesome book- detailed all the info, from hunting otters with dogs, to hunting fish with otters, hunting with bull frogs, shark harpooning, bow building. blowpipes etc etc
was my bible as a kid!