I've not done a quantitative analysis, but it seems to have been more frequently ruled as some sort of asset or commodity https://www.google.com/search?q=bitcoin+ruled

Exchange rate, also known as 'cost,' is a form of value.

But what makes something a currency? If in an alternate universe Bernie Madoff printed MadoffBucks and made agreements that you could use these as currency in some online stores and Pizza Hut, does that make it a real currency? Unfortunately I think the only way something becomes a currency is when a government calls it one.

It may not be a currency, depending how you choose to define that word, but it is certainly a fungible asset and a means of exchange. It acts both as a store of value and as method of transferring value from one party to another.