General opinion is that a side job is one that supports the main income of an individual, often times perceived as something that brings little money to add to what you make from your day job. If Mr X earns better from a side job when compared to the income from his career option, does the side job still qualify to be called a side job?
It is just a name, nothing more.
The real point of difference is which one is more stable and long term in the broader view of life. If you have a day job, you may be earning less than from some side hustle, but it is not going to disappear all of a sudden or stop paying.
In most of the third world, people are unable to follow their passion and this leads to this problem. Always make sure you support your family members so they can pursue their dreams, only then they will live happily and such thoughts will not cross their mind.
Coming to bitcoin's perspective, trading is something most of the users do beside their job and probably some are stock market veterans too. This aspect of managing money is a good thing and should be encouraged.