I pointed out to him that the commune had reinvented money, except that it was worse because it was worthless outside the commune. He was not happy with me for saying that, and told me I just didn't understand.

If outsiders had a significant demand for products made in the commune (including travel inside it), then commune dwellers could probably pay products outside in commune certificates or at least find willing exchangers for them into outside money.

Foreign trade and/or a significant amount of travel from and to countries is what makes the currency markets work. This would be a currency market, if either trade or travel could sustain it.