Okay, maybe we can be friends after all. :D
But trust me, I DID live in the city for 24 years, and something is just dead wrong with this scenario. Not criminally, just naturally.
If I had to speculate, I'd say the boyfriend got hit in the head, was a little dazed and thought that's as bad as it gets and starts walking away. Most guys haven't been in a fight since the 6th grade, so the shot to the head probably came as a shock. The shooter's jacked up on adrenalin, so when the actress challenged him, it wasn't that much of a stretch to pull the trigger, which shocked the people he was with...it's one of those deals where everything changes in an instant and all concerned want to replay that instant in a different way.
Again, the boyfriend should keep his trap shut.