CH, I agree with others that from what you wrote, it sounds like your kid has a square head on his shoulders and hopefully this incident serves as a 'holy shit' moment for him to realize how easily everything could have been flushed away. He is NOT invincible, and thankfully he had a pretty benign experience to learn that. How fortunate for him, and how reassuring for you to know that he takes DD responsibilities seriously.
Drugs and alcohol scare the shit out of me as far as kids are concerned.
I think I was partly naïve and partly too unpopular to get invited to places where drugs/alcohol were present in high school. I know it was around, but I've been a judgmental ass for a lot of my self-aware life and I'm sure nobody would want me around if they thought I would just narc/be a party pooper. (Note: i'm still a judgmental ass, I just keep more of it in my own head now and hope my face doesn't give it away.)
My stepson (13) is suuuuuper naive as well (I had to explain what 'bigot' meant this weekend, and he was honestly sad to learn/understand that someone might just be knowingly mean like that). He makes my younger self look like a rebel by comparison. He has the fear of I don't know what that keeps him straight in certain situations, and I believe our relationship and honestly with him in terms of being on his side/there to support him however we can will keep him from getting into a really boneheaded situation.
....stepdaughter (10) on the other hand. Holy shit. She means so well, truly, but she gets really wrapped up and motivated by peer pressure/attention for her actions. This has already led to some really poor choices with online communication in classroom social chats, and she's already felt the burn of having her conversation screen-shot and passed around to others. Thankfully because she's 10, the content wasn't as bad as it could be. Unfortunately for her, for 10yr olds it was still bad enough that her reputation is getting set AND parents saw it as well (because people monitor 10yr olds chatting). Husband has had to do a lot of smoothing things over with other parents so kiddo doesn't get totally socially ostracized from outdoor playdates, etc., as we work through some other things with her. I am scared to death of what this behavior turns into when she's 15,16,17. We're working with professionals to help address some of it now, but oh my gosh - it's really hard to feel like you're providing every positive resource, love, and support that you can and STILL know it's up to the kid to make the actual decision when push comes to shove.