I wonder if that was an old time thing to do. Marshall Carpenter seemed to use a little inside often also.There was one quote from the Patcheye interview that has stuck with me where he said something like "I know what an accomplishment is." It was a single statement that spoke volumes.
Getting back on topic, I read once that Greenleaf used inside English on a high percentage of shots. Someone earlier observed how the cue ball seemed to float from shot to shot, something CJ Wiley has remarked on as well when discussing his TOI method. I also wonder how much a factor the different composition of the balls used back then might have been in accounting for some of the unique attributes in his style of play.
Were they using clay balls in the 20s and 30s?