This is very solid advice. Once you become so productive that you don't need all of your working hours to do your job, you should spend that time on skill acquisition - either learning about something adjacent that you don't do daily or learn something that will be required for the next level (if that is your goal)

This is the only sane way I have found to progress in a tech career. The daily and weekly learning really adds up too - in my experience this is the difference someone who has 10 years of experience and someone who has "2 years repeated 5 times"