Bitcoin is an asset. Period.
On the other hand, it depends on what you call an asset.

Check the definitions below:

https://www.investopedia.com/terms/a/asset.asp

https://www.investopedia.com/terms/b/bitcoin.asp

"Like any other asset, the principle of buy low and sell high applies to bitcoins.The most popular way of amassing the currency is through buying on a Bitcoin exchange, but there are many other ways to earn and own bitcoins. Here are a few options which Bitcoin enthusiasts can explore."

Read more: Bitcoin https://www.investopedia.com/terms/b/bitcoin.asp#ixzz5R5vjpfLx