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?
Definitely Yes, it is only called a side job because you have a main job. Even though job A brings less income over job B, both are still considered a job. It's just that one is your primary job, wherein you fully commit your day time while on the other hand a second job or side job is where you use up your extra time that brings income to your daily. Having a side job both have risk and consequences, but it is still profitable. It will only depends if you are satisfied with your income on your primary job or you want to increase it and your job isn't allowing you to increase it so rather than waiting for a promotion you find a side job that will satisfy your want of increased salary.