Just my interpretation: that programmer is a professional. They are paid to do programing. They are still professional even when they are working on their hobby project, because it is not a function if they are paid for that particular code, but if they are paid for any coding at all.
If that programer would go and coach their friend’s basketball team for free they would be an amateur coach, but they are still a professional programmer even while coaching.
If that programer would go and coach their friend’s basketball team for free they would be an amateur coach, but they are still a professional programmer even while coaching.