Don't Second guess yourself on this one, expecially since you didn't have a weapon on you at the time. you did the right thing by calling the police, and reporting the incident and what they were wearing. In a situation like that, getting out of the immediate area is always the best course. even if you had had a weapon, you didn't know for sure what was going on, you could have blundered right into a gang fight, or something like that. I think you did extremely well, expecially considering the amount of detail you was able to memorize in such a short time. Just because we carry weapons, doesn't mean we have to intervene in every situation we come across.