Contact in the ball and socket is a normal occurrence. However, there are points around the edge where there is a transition from soft to hard structures, and these points can pinch the cuff or bursa. When that occurs, pain and inflammation can start. If the pinching goes on long enough or with enough force, it can cause abrasion or even tearing of the rotator cuff.
Pain generated from an injury of the shoulder can send signals to the muscles of the shoulder to limit activity. During an examination, this can test like a rotator cuff tear. When the injury heals or is treated the muscle no longer receives the signal of an injury and returns to full activity.
This is common with impingement and bursal inflammation. It is also common after surgery.