That woman's an idiot. Castle Doctrine had nothing at all to do with anything. That was straight up self-defense analysis. The intended victim was armed as he had a right to be. The other guy drew a gun on the intended victim. The intended victim (having done nothing wrong) beat him to the draw and won the gunfight.
Actually, the Castle Doctrine has lots to do with that.
It means you can defend your property, and have no legal duty to retreat. In states that don't have that, the victim has a legal duty to run away before deploying deadly force.
Castle Doctrine is similar to “stand your ground,” but is typically limited to real property, including a person’s home, property and, in some states, cars or workplaces. The concept is that an individual has a right to be safe and secure within his or her own home or “castle” and should not have to retreat from his or her home in order to be safe. Depending on the state, an individual may have the right to protect himself or herself, other people, and his or her property by force — in some instances even employing deadly force against intruders without retreating.
Good point, but the reason I say it's a non-issue in this case is that there was no opportunity to retreat. When someone draws a gun on you with intent to use it, you cannot outrun a bullet, so even if there was no castle doctrine, you'd have a right to draw and fire under any law in the land where you are permitted to be armed. In fact, even in a place like New York, you might find that you're charged with illegal possession of a weapon, but still not be charged with murder, due to the straight up self-defense circumstances of the case, castle doctrine or no castle doctrine.
Castle doctrine applies where you are aware of a deadly threat in advance, and have time to escape. Places without castle doctrine require you to even exit the house, if need be. But even where there's no castle doctrine, you can investigate folks making a ruckus in your yard, and if they draw on you, you can shoot them in self defense, because you cannot outrun a bullet.