this has nothing to do with Stand Your Ground, that law is there for you to defend yourself in danger; not go out looking for it.
Just like any good Attorney would do, the stand your ground law is simply being used as a defense. The law actually has nothing to do with the events that took place. No where in the law does it mention you have the right to start an altercation, in this case following someone, and end it with deadly force.
If the only events that took place were Zimmerman walking back to his truck and Martin attacked him then Stand Your Ground would apply but we all know that is not what happened. Zimmerman followed martin with a loaded gun in a truck and on foot.