Not a all. PoS is a technology, like PoW is.

Making it mandatory to use this particular crypto would make it fiat. Fiat means "let it be done" (like fiat lux) and, on the particular topic of currency, it means that a currency have been established as legal by decree.
Any currency that has value from obligation (decree) instead of actual value is fiat. If a government can hardfork at will and not let users decide if they like it or not, this is fiat. Banknote or cryptographic token, this makes no difference. And the exact protocol (PoW, PoS, PoB, PoI, PoT...) makes no difference.