Studies of the Mangareva language in the 1930s recorded that it contained specific words for 10, 20, 40 and 80. Sort of like how English has special words "dozen" and "score" for specific quantities. Their culture and language has been nearly obliterated by external influences over the centuries, so all that remains is the fact that they had special words (beyond their normal numbers) for those values. That could be pure coincidence, or it could indicate that they worked with binary numbers and thus had special words for 0b0001, 0b0010, 0b0100 and 0b1000.
The thing that doesn't make much sense to me is why they would have multiplied their binary digits by decimal 10. Instead of special words for 1, 2, 4 and 8 they have special words for 10, 20, 40 and 80, and that doesn't make any sense mathematically. Unless originally they used binary and had special words for 1, 2, 4 and 8, then gradually adopted decimal. The special words for such small numbers wouldn't have been useful, so the meaning switched to indicate 10 times that value. 10, 20, 40 and 80 would be useful quantities to have special words for when it comes to trading, buying and selling, and even talking about a person's age.
Either way, it sure seems to hint that they used binary math at some point in the past.