Many great thinkers from history were interested in questions that today would be called "psychological." what did these pre-psychologists have in common with modern psychologists

Psychology is a scientific process to understand the thought process of the human being.  

The common thing between the pre-psychologists and in modern psychologists is the methodology to understand the mental conditions, feeling and emotions of the human being.

Explanation:

In Ancient times, mostly Psychologists were using the Yogic way to understand the feelings and emotions of other's mind but in modern time there are many ways to understand the same things.

We can also use many technological devices to get the psychological conditions of others.

But either in Ancient time or in modern time, the preferred methodology is almost the same.