What this is missing out is the fact that there are now digital currencies of nations as well, for example petro which is still digital currency but at the same time based on a nations resources so it can always be combined.
Bitcoin was never the first digital currency, it was only the first one that seen this much adoption, there was e-money type of deals before that never got too big because they never had blockchain behind it, what made bitcoin original and unique was the blockchain, otherwise digital currency has been as old as internet itself, even data was seen as money at one point and exchanged for fiat currency to be used. Hence there are other smaller details that should be invested some research into before this theory could be 100% done with.
I guess Cryptocurrency is digital currency. Fiat currency exist in digital form too, so it definitely qualifies as digital currency...maybe it should be considered partly digital.
Some websites tend to define digital currency as currency that exist purely in digital form. I wonder why this is so.