They may be talking of this new, decentralized, open-sea, counterfeit-proof currency I've heard fishermen raving about. It's called cowrie. But some friends working in the mines think it's a joke and it will soon crash.
Silver in standardized amounts as a form of payment is attested before the Hittites are. (The same goes for grain, obviously.) Cowries as payment are from an entirely separate region, but presumably were no more difficult to produce than smelted metals were.
They even started to make some meme cowrie shells in China.