Look at it this way. A person may know how to wire a house, but only a certified, competent, licensed electrician can actually do the job.
You grok?
Yes, I grok. And knew a lot of the folks who wrote the California laws for psychologists of that era. Professors were NOT considered to be “wiring a house.” They were considered to be only in their turf of academia teaching. And as such could also fittingly be called psychologists whether they were strictly teaching or doing research and teaching. At that time. Evidently things have changed.