When discussing semantics, I believe the etymology is often more important than quoting modern authorities.
...from Latin, fiat "let it be done" (used in the opening of Medieval Latin proclamations and commands), third person singular present subjunctive of fieri be done, become, come into existence," used as passive of facere "to make, do"
One could certainly argue that the 50 coins in the genesis block were created by fiat. Indeed, "fiat lux" is a famous phrase from Genesis, the name alone suggests such a comparison. It is harder however to make that argument for coins mined today. Nobody has the power to issue new coins by fiat, they come according to schedule.