I agree, at least from what I've learned so far.
Martin reacted the same way I would have if put in his position. He tried to avoid this hostile stranger, but this belligerent "creepy-ass Cracker", insisted on hassling him. When he felt cornered, he attacked--in self defense. Ironically, he was perfectly within his rights under Florida law: he was "standing his ground".
It sure looks like manslaughter to me, but I can't imagine Z being convicted of murder on such flimsy evidence. He'll walk, or he will be convicted--of a crime he did not commit. Either way, justice will not be done.