Im not sure if that proves it's a "currency" rather than an investment. The irony is, bitcoin was suppose to be an alternate grass-roots form of currency, but because of the way the cryptocurrency market works, it ends up being more comparable to buying and trading stock. It's like owning property in a booming area. You aren't going to sell, because you know holding onto it, it could triple in 4 years. That doesn't make the housing market a currency, it makes it an investment based on the fluctuation of the bubble and the market.