Whether you use an altcoin (or bitcoin) for a long or short-term investment, or because it satisfies you as a medium of exchange, it'd be misleading to call it a "currency". I don't know who began this terrible start of the use "currency" after "crypto", but, in my opinion, it shouldn't be formulated like that since none of them are currencies.
A currency is a system of money in general use in a particular country. For example fiat. Fiat money gives central banks greater control over the economy because they can control how much money is printed. This is how the state works.
For the sake of discussion, I'll ignore the fact that you are many years too late and this naming won't change.
I'll come to the fact that your... assumptions... are wrong.
Merriam-Webster doesn't take country/government in discussion when it defines currency. Even more, it tells that in the past even furs were used as currency.
1
a : circulation as a medium of exchange
b : general use, acceptance, or prevalence
// a story gaining currency
c : the quality or state of being current : currentness
// needed to check the accuracy and currency of the information
2
a : something (such as coins, treasury notes, and banknotes) that is in circulation as a medium of exchange
b : paper money in circulation
c : a common article for bartering
// Furs were once used as currency.
d : a medium of verbal or intellectual expression …
// neither side possessed any currency but clichés …— Jan Struther