Will Smith was not in his car, he was walking toward his car I assume since he was shot in the back and side. Yes, he died in his car after being shot outside the car I assume. I am waiting to see all the facts. By will smith claiming to get his gun and have a loaded gun in his car can be perceive as a threat. If Hayes got out his car with his gun and approached will smith then you absolutely correct stand your ground will not apply

In the United States, a stand-your-ground law (sometimes called "line in the sand" or "no duty to retreat" law) is a law that authorizes an individual to protect and defend their own life and limb against threat or perceived threat.

https://en.m.wikipedia.org/wiki/Stand-your-ground_law