What happened to my lung?

Your lungs are actually a little like bubble-wrap in their make-up. And they're surrounded by a sac-like membrane called the pleural sac. Partially collapsed lung is a good possibility. Scarring from tear/damage would set you up for bacterial infections later on, especially if that part of your lung can't expand properly. Another point: your bones and tissue, especially bones, conduct sound. You hear things happen inside your body sometimes such as a bone breaking (ugh), so your perception of the sound would still be different from your buddy's take on it. Your description of the popping bubble wrap is a clue that something did actually 'pop'. Ask someone who has torn a muscle in their back or chest wall; often it is described as hearing 'a tough balloon breaking' in slow motion. (Ugh again).