Should I add a vapor retarder to an interior cinderblock wall as part of my basement remodel?
Are you sure it was mold? It may have been mildew. In my experience, mildew can grow on nearly any surface as long as it stays moist...be it bare concrete or painted concrete.

In this case, the moisture on this interior wall likely is not coming from outside the basement, but rather is moist air condensing on the cool concrete. Painting it won't stop that from happening. 

If there were existing finished walls, the issue was that moisture was getting back there, condensing, and then not easily drying. Leaving the walls bare (ie, no finish wall in front) would allow them to dry. 

Alternatively, you can certainly spray-foam them as well. This will prevent the moist air from ever hitting the surface of the wall in the first place.

A final thought would be to check humidity levels in general. You do want to keep the humidity below about 50% and that's often hard to do in a basement without a dehumidifier. So be sure to have a dehumidifier running down there as well.