In an economic sense,
An INVESTMENT is the purchase of goods that are not consumed today but are used in the future to create wealth.
In finance
An INVESTMENT is a monetary asset purchased with the idea that the asset will provide income in the future or will later be sold at a higher price for a profit.
I really don't want to turn these into an economics class but the both definition of what investments are clearly should settle the argument of whether BTC is truly an investment or not.
to my own opinion and point of view, bitcoin is both asset and currency even when people do buy and storing BTC some other still used it to pay for goods and service so to does who used it for business purpose it a currency to them why does who buy and store is an investment to those categories so don't be so confused with it complicated used.