Let's put aside "competing with an employer", because the majority of us would agree that if you take the King's shilling, you shouldn't also be employed by the King's enemies.
Let's also put aside the key term backing the supposition of this article; "anecdotal evidence" which is an oxymoronic term, because without data (specially when writing an article on a population as big as all working adults) anecdotal evidence really is just conjecture.
Now, let's also all admit that there are people who outsource their jobs or more likely parts of their jobs to others. Right or wrong they are taking advantage of simple location arbitrage. This is one reason why staff augmentation services are on the rise.
But, what is important in Talila's example is that this individual was not performing at the level to which he was compensated and for which was expected of him.
Side hustles which do not compete with an employer are fine. In fact, I think that what has been shown during the dot com burst, great recession, and the recent spate of lay offs, is that side hustles are essential because the relationship between employer and employee has significantly changed since what it was at the beginning of this century.
Gone are the days of true entry level jobs. Companies have responded to the fact that the majority of millennials and gen z's leave their first job within 1 year of starting. Why should a company spend time and money training a person who isn't going to stay?
(My belief is that you train and give as many opportunities as you can so an employee/team member can you leave you, but compensate them and treat them well enough so that they don't want to leave.)
Gone are the days of company loyalty to an employee. Every tech company would outsource their tech talent to India and other low cost areas if they could. But they can't. However, when employees see that their company is actively trying to outsource their and/or similar colleagues' jobs, not having a non-employer competitive side hustle makes little sense.
Lastly, gone are the days of the "40 hour work week" (I honestly wonder whether or not they ever existed, but that's either illustrative of the change that happened before I entered the job market (I came into the job market when unions outside of government and the auto sector were on their last breaths) or has always been that way for salaried individuals.
Companies have trained their employees to not regard their compensation based on how many hours they have worked, but rather on what they deliver.
When compensation is tied to delivery rather than how many hours are worked, a non-employer competitive side hustle that can be done without impacting an employee's deliverables makes perfect sense.
Overall a treatise could be written on just this topic. The question is, what can be done to mitigate acts and weaknesses that these types of activities can have on employers while working with employees to facilitate non-competitive side hustles.