to correct the OP
currency is anything used as a medium of exchange
MONEY is a specific currency used by a community/nation and ratified as the official currency of that society.. money in history has been controlled by the rulers of that society and distributed/taxed and accounted by those rulers(legal tender)
much like europeans claim euro as their money, much like americans claim dollar as their money
we in the bitcoin community/society deem bitcoin as OUR money with a different method of distribution and control..
but europeans do not claim dollars as europeans money. but still recognise dollar as a medium of exchange foreign currency vs euro
Is simply because the market price of bitcoin is highly volatile and subjected to large price swings. as a result,the market price at any given time may vary wildly from what could be considered a fair value.