I graduated from high school in 1972. One of my teachers way back then said he drove truck during the summer. Makes sense. You “take the summer off” if you can afford it. It doesn’t look like this guy can.
I graduated in 1975. ALL of the male teachers and some of the female ones I knew took summer jobs. Some in house painting, light construction, driving detassling crews, some for the school district on textbooks projects, teaching summer school, teaching other classes for the park district, some lawn care businesses, etc. But back then in IL, it was probably more likely to be able to do that kind of work on a temporary basis, without unions shutting them down.
Several people with whom I went to high school became teachers, and have retired at or before age 60, with ending salaries in the $90Ks, at a minimum.