You did the right thing. That kid is probably grateful that you were there. If you would have went to get help first, he probably would have some serious damage to his hand.
Your arm sounds like it hurts pretty bad. It's probably swelling more than anything. But if the pain is real bad, go see a doctor. If you aren't one to abuse pain meds then by all means, take whatever he gives you until the pain goes away. Sounds nasty. I would go either way, just to make sure there's no problem.
Again, good thing you did bro. We all complain about guys like that in the gym who don't know what they are doing and how they are distracting. We were all newbies once. Maybe more of us should take time to help others. I remember something similiar happened to me when I was 18. My first time in a big commercial gym and I didn't know the olympic bar was 45lbs. I overloaded it, and got trapped doing close grip presses. A guy who looked like a vet came and helped me get it up and then without making me feel stupid helped me load a lighter weight on and then helped me with my set. If it weren't for him I probably would have been to embaressed to go back there again.
Besides all of that, how is the cycle going so far?