So, based on that definition, it is true that Bitcoin is not a fiat currency because it is not given value by law or government. However, although it technically does not have a centralized issuing authority that can arbitrarily create Bitcoins, Satoshi Nakamoto did hard code a creation rate for Bitcoin. In a sense, he is the original issuing authority. The only difference between Bitcoin and fiat currencies, when it comes to currency manipulation, is that Nakamoto committed early on to a specific plan for issuing currency. The government (or the Fed) not only does not make that commitment, but it is unable to make such a strong, unbreakable commitment, although it verbally makes similar commitments all the time.