Slightly different scenario to think about would be.
Person A yells at person B.
Person B does not get out of truck, but yells back.
Person A shows gun.
Person B shoots person A.
Person B by not leaving truck is legally covered by castle doctrine because of "brandishing" threat of person A.
Person A yells at person B.
Person B does not get out of truck, but yells back.
Person A shows gun.
Person B shoots person A.
Person B by not leaving truck is legally covered by castle doctrine because of "brandishing" threat of person A.