There's a lot of distinct differences that could be drawn between the two.

1. Fiat can be created from thin air; cryptocurrencies has a set amount of coins to be mined/acquired.
2. Inflationary (fiat) vs Deflationary (cryptocurrency)
3. Region-restricted purchases (fiat); shopping with no borders (cryptocurrency)
4. Requires an intermediary to store money (fiat); you're your own bank (crypto)

These are some of the things that differ crypto from fiat. There's a lot more aside from those things but that's just what I thought off the top of my head.