Not necessarily. It would have to be an investment account to be considered capital gains. An example of a foreign account where growth could be considered as investment activity would be for a foreign account holding cryptocurrency. When the units are traded, then a taxable even would have occurred. However, careful recordkeeping is needed so that deposits are not considered gains.
Otherwise, it would not, as a rule, be considered capital gains to have an account increase in value.
IRS: FAQs on Virtual Currency Transactions
IRS: Cryptocurrency Wallets
IRS: Virtual Currencies
Mining Bitcoin Taxation
