I believe the human voice is the most popular instrument, world wide by a long shot followed by clapping. You are probably right that most drums are inharmonic, but I wonder what percentage of percussive instruments have a strongly identifiable fundamental anyway (or some tone if not the fundamental). At any rate, perfect intervals sound really consonant in singing, so I'd expect a bunch of cultures to independently stumble into that knowledge because singing is so popular. I didn't read the actual study, but I'd lean towards distrusting a single study or two, and in this case, wonder if this group of people is into polytonal singing.