In a conscious patient there is almost always an element of activity in a movement that you impose on a patient. In fact getting the patient to allow you to perform a true passive physiological movement (ie a movement they relax fully allowing you to perform the movement but which they could do themselves) is actually quite a motor skill and in some patients almost impossible to do. Getting the patient to relax is key so I agree with your instructor that you need to facilitate this by putting them in a position to fully relax (ie usually supine with a pillow supporting head and neck, posturing the shoulder in a pain free position - often in a few of degrees flexion and abduction and avoiding rotation). It isn't really enough to tell them to "loosen up and relax". In a sitting and standing position the scapulo-thoracic and and rotator cuff muscles are rarely completely silent as they preserve the posture of the shoulder complex, including keeping the humeral head optimally aligned in the glenoid fossa.
As far as appropriateness of the treatment it sounds ok to me. However I think you need to understand what the surgeon has done and the effect that such glenohumeral movements will have on the tissues in or near the subacromial space. I wouldn't want to contradict the surgeon's communication. However I think we should be mindful that early active movment may be better, providing they are gentle enough not to excacerbate the inflammatory/healing processes. Sometimes surgeons give blanket injuctions not to actively move as they don't want therapists or patients to be too enthusiastic and thereby be detrimental to the healing process. However getting the rotator cuff muscles to contract and low loads and through small ranges concentrically or else statically may promote a better and improved functional outcome.
I would be interested to know if MSK physios out there agree with me?