The assertion that Bitcoin is a fiat currency is a bit dubious. To make a decree, you really need some "authority". It wasn't Satoshi's decree which made Bitcoin a currency; it was the fact that people accepted it and started using it that made it a currency. If nobody used it, it wouldn't matter how much Satoshi declared that it was a currency - it still wouldn't be one. However, when the Ecuadorian government declares that dollars are legal tender, and taxes will be paid in dollars, that means people have to use them, and they are a currency whether you like it or not.