Bitcoin goes beyond the traditional definition of currency.
Its a bit like PayPal, where you can transmit a set monetary value across the internet from one recipient to another. It is an encrypted blockchain system that transmits net worth, so technically not a currency, in the legal tender aspect sense of the word. But at the same time it does have value like a commodity, like gold with its value set by an exchange rate.
Maybe we need to redefine currency instead of debating whether bitcoin is a currency.
This is basically true.