In this guy's case, there is very relevant case law. Before March 2015 Migrationsverket applied the rules based on the average of your work visa period, 2 years. They would take your last 2 year's salary, divide by 24, and see if it's over 13,000 kr per month. After March 2015, following new case law, they started looking at each month individually and deporting if any specific month violated the rules.
Depending on when he did this, it is possible that if he asked a migration attorney for guidance they would have approved, and they would have been correct. The rules retroactively changed that year. It still would be just as likely to make the wrong decision after the court ruling, since migration court rulings aren't a particularly big topic of conversation for most people. Nobody really learned about it until deportations started skyrocketing in 2016.
I wrote a bit about the topic here: http://dontdeportthedog.com/wp-content/uploads/2016/11/Failu...