then US dollar is also an investment.
i'll tell you why. where i live the value of local currency is dropping so there are many who are now buying USD to stay ahead of the inflation that is going on. in fact they are investing in USD. and what they are doing matches the description you posted here, they will sell it in the future to get a huge profit.
but it doesn't make USD an investment. US dollar is still a currency no matter what you do with it.
the same thing is true about bitcoin. bitcoin is a currency by nature even if majority are using it as an investment.
I think that it's a matter of how you view the things. I've done the same with Deutsche Mark in the past, when inflation in my country was much bigger and I also had some liquidity.
Keeping DM in the bank at 0.25% rate gave some +0.2% profit in DM.
Keeping local currency in bank at 20% rate gave some -5% profit in DM (maybe the numbers are not very accurate).
Keeping local currency at home... ouch!
Since I've done this for profit (also to not lose money) I've also seen that move as an investment.
And yes, I also see Bitcoin as a coin and also as an investment. In my eyes the two concepts can coexist.