You are not LEGALLY required to do so, but I think it would be wise to do so.
Someone may have seen you draw down on the BG, or the BG might try to call the cops and accuse you of something. Then you are driving/walking down the road minutes later and several officers initiate a "felony stop" on you.....not a good feeling I wouldn't think.
If the situation was serious enough for you to draw your weapon, it is serious enough to take the time to report it to the cops.