I did see that mentioned while reading Wikipedia, but I dismissed it. It is a third-hand report from decades (someone told someone who told me who tells you) previously about a method which may - like the Easter Island 'invention' of writing - simply have been copying foreigners either directly or indirectly and so even at face value doesn't establish the claim. I don't think such a dodgy source is enough to overcome all the reports and circumstances (eg. described cumbersome system of firekeeping seems to be less likely if knowledge of making fire had been retained).