Bitcoin is sound money as you can convert it in real cash in just 10 minutes in an exchange. If you are in Europe for example you can do so from bitpanda.
Bitcoin is sound as you and only you are in charge of it and it has no central authority to make decisions about it. You are your own bank. In this sense bitcoin is the most sound money that exist out there ( in the internet).
Your first line describes it as an asset which is not the same thing as money. Money implies you are using it directly without exchanging it and for me there are some cases of this but the vast majority of bitcoins are held as an asset and not as money.
The thing is, the people that use Bitcoin like to treat it as an asset instead of an investment and that is why they keep spending Bitcoin like they are with an actual currency. I would make the most money that I can and try to have Bitcoin on the side just in case the price of Bitcoin goes up.