Presumably the fiat part comes from the power to create legal tender laws or the power to collect taxes denominated in a currency, or both. Cryptocurrencies don't have either of those powers.

That is, a fiat currency's value isn't based only on objective or subjective/speculative value, but also, to an extent, on the issuing state's power to require people to use or accept it in certain transactions.

The dollar only has value because you are forced to pay the government with it to pay taxes or else you go to prison/get beat to death for protesting. The nice thing about crypto is the absence of a mafia threatening my life if I refuse to use it :)

It's part of the cult-like mind game that underlies cryptocurrency communities.

The in-group must signal its faith by using certain words in the opposite sense of their usual meaning. Bitcoin is following the Scientology playbook here.

Are you implying it could be attacked? Isn't decentralization in general, maybe not in case of BTC, a key factor that would put it into a societal hive-mind and out of physical realms of army's influence?

Technically it's a fiat currency because people trust the code base and by extension they trust the development team.