I think they are just saying that it is the new currency because it is becoming popular and widely accepted in some countries. Bitcoin is not really a currency but a digital currency in which it is decentralize and volatile.

Bitcoin is used in some payments and others, if you search the meaning of currency it is a currency that is being used in a country as a their main means of payment and not only that, currency also means that it is accepted or being used. Bitcoin is not a main currency of one country but it is accepted as such.