What he suffered is a typical burned-out that many of us may not realize until much later in life, say, in our 40s or 50s, which would then be called "Midlife Crisis." It is high schools' fortune to have new blood like him.
ps. I am definitely not as smart as Dr. Zhao. I only thought about quitting research when I was in my late 40s. At that time, I thought very hard about what I would do next. At first, I thought about teaching high school math/sciences. In fact, I was offered a summer teaching job after I applied to two top private schools in Honolulu. I chickened out, because the students in a summer math class may be from other schools, including public schools so their math abilities would be a mixed bag. Another reason was the lack of freedom in terms of time, as many research jobs do not require you to work in your office... Of course, I did consider teaching high school would be a waste of my training as a numerical ocean modeler. So, I finally ended up starting my own business, as a freelance English editor...