The definition and use of the word fiat is interesting, in Latin it means "let it be done".

You could say that the creator of Bitcoin decreed that it had value (I'm not sure I would agree), but it's still different from government backed money because nobody is forced to use Bitcoin (to pay taxes for example).

It certainly seems that within the Bitcoin community the word fiat now means government backed money, I suspect if Bitcoin becomes more successful it may end up redefining the word.