They are wrong if they think it is investment money that they can use to multiply that money because it is not an investment. What's called an investment is they have to use a certain amount of money, not use it for anything, and only save it for a few years. Later after several years have passed, they will see how much the value of the investment they made a few years ago. And so far, it's bitcoin that can be a suitable investment for them. But in gambling, we have the opportunity to lose, even though we can also win, but it won't be as much as if we lose.
If the gambler only holds BTC in a gambling account without using it to gamble then it includes investment, but it is recommended that each investment is managed in a personal wallet and does not trust investments in gambling accounts even centralized exchanges, for gambling you must determine the lowest allocation of funds for gambling because gambling is not chasing profit but for entertainment in spare time, if you lose then you don't have bad impact on your BTC investment in personal wallet.
Indeed, it is an investment, but it is not a good investment because we do not know how long the casino will operate and whether the casino can maintain the accounts of each of its members. It's better to manage the investment in a personal wallet because all the assets will be in our control, and we are fully responsible for all the assets. As for gambling, we should have a special budget for gambling so it won't interfere with the allocation of funds in other places, and we can control our monthly expenses. Thus, we can enjoy every piece of money we have while we prepare for our future by investing in bitcoin.