The analysis isn't whether or not the other person got angry, it's whether a reasonable person would perceive the exchange as instigating or asking for a fight. Some people use anything as an excuse to get angry, that is, they come to anger unreasonably.
From my impression of how the physical confrontation started, I don't think the "stand your ground" principle is in play, at all.
I would agree with you there. If one were attacked from behind and knocked to the ground then pummeled by an assailant much larger than you, standing ones ground is no longer in the equation. It has now become a matter of survival........
"Stand your ground" presumes that you have an avenue of retreat. Mr. Zimmerman did not, he was on his back with his assailant on top of him......