First of all, don't walk, run to see your Bishop.
Second, if he asks who the guy was, tell him! By our being afraid of saying I'd guess that he's known to the Bishop, you need to pay attention to what happened, he sounds like the instigator and for all you know he may have had previous issues known to the Bishop, so the Bishop needs to know.
Beyond the Bishop I doubt anybody will know. I'm an Elder's Quorum President and I occasionally know when there is a situation, but I never know what it is because I don't need to.
It's likely that he will thank you for coming in, talk to you about what happened, and tell you that he's proud of you for stopping it before you went all the way (which isn't easy to do!)
Disciplinary actions depend on a number of things, as a local leader/returned missionary/ temple married father who grew up in an active LDS home my punishment would be far more severe, under your circumstances it's not likely to be any major deal at all, I would be very surprised if it went beyond a talk with the Bishop.
So my last advice - drop this question and pick up the phone - he can help you, we can't.