If being a passenger eliminated responsibility for aggression, most drive by shooters would be innocent.
Do we have to view the two shooting scenes as two separate incidents? Doing that makes each side an aggressor at different points. Viewing it as one incident that spread out over time and space, makes BM the aggressor since he brandished his gun first.
Adrenaline can cause people to chase after someone after being attacked even after being safe. I've only been in one fight in my life, back in middle school. She was the aggressor. She hit me. I jumped her and I continually went after her long after she tried to get away from me. I even hit a teacher who was trying to separate us. I just kept lunging back at the girl. The fight started near a locker and ended in a classroom a few classrooms down the hall from where it started. I did NOT know what I was doing once my adrenaline kicked my fight/flight response. There was no actual thinking process about safety or tactics. The body just reacts.
That's why I view the two shooting scenes as one long prolonged incident, not two separate incidents were the aggressors changed roles.
BBM. No, we don't have to.

As SpanishInq said upthread, a lot of that would depend on how good the legal representation is.
There's no single bright-line definition for when it changes from one incident to two. In general, the greater the break -- in time, in physical distance -- between two things, the more likely it is that they'll be viewed as two separate incidents.
If the Audi had waited an hour, then gone to the cul de sac, that would be pretty darn likely to be viewed as a completely separate incident.
If the Meyers car had fled to their home 20 miles away, and the Audi followed them or pursued them that distance, that would be pretty likely to be viewed as two separate incidents.
If the Audi stopped shooting (at the first shooting scene), and the Buick didn't move, but sat there, waited 30 seconds, and then started shooting back, that would (IMO) be pretty likely to be seen as one single incident.
If this case ends up in court, and
if it's defended as a self-defense case, and
if it hinges on who was the aggressor at the cul de sac, I would imagine the attorneys will spend a fair amount of time on exactly how far it was from shooting scene #1 to shooting scene #2, and how long it took to get there, and things of that nature. If EN takes the stand, or if the driver takes the stand, I'm sure there will be questions like, "Did you, before you turned into the cul de sac, think about just going home?" and "Did you still feel that you were in danger from the people in the other car" and so forth. Defense would be trying to minimize the break between shootings, and prosecution would be trying to maximize it. IMO, JMO, MOO, and all that jazz.