He doesn't say nothing was really proven - he just says that they didn't establish whether this dislike of dissonance was innate or not. That wasn't what the experiment was about. It was to find what caused the dislike - and they ruled out 'beating' and propose it's harmonicity. It's also not beating per se which people find unpleasant but rapid beating -roughness. Does Gamelan try to produce 'roughness'-ie rapid beating - or just beating - which I could imagine would be quite cool.