That’s not right. Not every speculative investment vehicle can function as money. To function as money something has to be divisible (e.g. cut a dollar into cents, cut a kg of gold into grams, cut a Bitcoin into bits), it has to be fungible (any unit of it is the same as all other units, i.e. a dollar is a dollar), it has to be portable (you can put a gold coin in your pocket), it has to be easily-transferable, it has to walk the razor’s edge between plentiful and scarce, etc.

The other big one is wide acceptance, meaning many different people being willing to accept it as payment for goods and services. You can argue that Bitcoin has achieved this as well, though maybe not as much as one might wish or dream.

Bitcoin was designed to be money, so it has the properties of money. That’s not true of pretty much any other type of speculative investment.

Edit: added more to first paragraph.