No, absolutely not. Some of these "stand your ground" laws leave a whole lot to be desired - putting it mildly. This was a hot headed man who felt he had the right to boss these kids around. He didn't like the fact the kid gave him lip and he grabbed his gun and started firing. The racist statements he made from jail make it even harder to believe that this was a "threatening" situation and point to the most likely scenario, that this was an angry white male with preconceived notions about young black men. When they ignored his demands he got angry and reacted instead of being rational.
In his paranoid mind could he have thought those boys were going to attack him? Perhaps, but here is my problem with the whole standing your ground thing - it doesn't require people to be rational at all, they can overreact due to their own preconceived notions and claim they felt threatened. That kind of madness is going to lead to a lot more incidents like this I'm afraid. I find that very sad.