I don't think so that holding is a form of gambling. Gambling involves game wherein you can win or lose. Holding is just your strategy to make profit so with this you need to always check the market to monitor it's price not like in gambling. In holding once you can't sell your bitcoin during its high price only the profit will lose not like in gambling that if you lose the game you don't have profit and you lose also the capital so you need to go back with nothing. So gambling is worst than holding.