For me currency and asset is same . bitcoin is asset becuase many people keep it for their future money and because of this value people use this to buy anything that they want like paying bills or buy a stuff . bitcoin is currency becuase bitcoin give a profit to us .
I somewhat agree to this that they should be identified in the same categories but for me under different type since bitcoins is a currency by its nature and how it was established to assets were supposed to provide you something of value which in return will give you currency so they go hand in hand. Bitcoins can be an asset but in some different scenarios a currency because of its very high value it appears to be too much to be just spent instead investors sees it as an asset and prefer to hoard and hold it for future market purposes in case the prices go up.
Bitcoin is currency since it fits the bill perfectly, we could argue that there is nothing in the world more suited to be a currency than bitcoin, so if bitcoin is not a currency then nothing is. But it is also an asset since its price is increasing highly in short amount of time, it is offering the opportunity to making money just by holding the coins.