Torn Rotator Cuff

I am 49 years old, I don't smoke, or drink. I am within my ideal weight, and I exercise regularly. Last October I was given a flu shot in to my shoulder, and slightly on the backside of it. It was given very high. Right after I got the shot I went to the gym to work out, and was lifting light weights on the nautilus machine(20 lb total). I experienced immediate pain in that same shoulder. It was unlike anything I had ever experienced before. Two weeks ago, they finally ordered an MRI. I have tears in my supraspinatus, and infraspinatus muscles, and a perforation in the shoulder tendon. I have had flu shots before, but have never had this problem. The medic giving me the shot was being instructed by a nurse at the clinic. I believe that it was done improperly. I am now in physical therapy, and recieved a steroid shot for the pain. I am going to have surgery soon. My questions are this- could it have been improperly administered, and did the exercising after the shot aggravate the shoulder? Is it possible that the two are related?