Actually anything that can generate income to you can be called a job. However it is said that gamble can not be called a side hustle and yest it's true but there are folks that do make money from it consistently. Although there are times which a trader makes profits and there are times which traders don't and likewise gamblers too.
So my point is as long as it can generate money for you without any huge losses it can be called a side hustle.
It is completely true, as long as one’s activity brings stable income, and does not lead to high losses, then one can speak about the side job. Admittedly, gambling may be different from other jobs but the reality is, there are people who have been making money from other risks-related operations on a continuous basis. It is the same with the cases of trading since the world has the opportunities to earn and increase, there are also risks of getting a loss. The question here is, what does the difference a person make in relation to handling the risk and the ability to know when one has ventured enough. Although evaluating its earnings do not result to continuous losses, anybody has the right to claim that it is an acceptable side hustle.