What is involved in the discontinuity hypothesis is the recognition that the people of the Middle Ages and early modern Europe did not regard as belonging to a common category activities (hunting and gambling, for example) that are usually classified together today under the heading of leisure.
In the sentence, those people did not regard { which thing} as belonging to common category activities. Moreover, Hunting and gambling are common category activities, and these are called leisure. Even if my interpretation is correct, I am unable to find the object of regard.