An investor according to Oxford dictionary is a person that puts money into anything with the belief of having a financial profit in the future. This clearly shows that your friend is a bitcoin investor by nomenclature. But with bitcoin there’s more and that is to it than other investments. For one to be a proper investor of bitcoin although it was just a payment gateway according to satoshi, then one needs to learn lots like it’s security and also the trading abilities of it like when to buy and when to sell these coins. The kind of exchanges to deal with and also the kind of wallets to store them in.