Ken, I thought Zim's narrative was that the 911 dispatcher told Zim to not continue to follow Martin; and that Martin confronted Zim as Zim was returning to his truck/car.
If Zim was returning to his car, this was a better thing to do than having a confrontation with a suspicious character who might be aggressive or armed. If the fellow was up to no good, even just attempting to have a pleasant chat could be confrontational.
If Zim had done as you suggest, is it possible that Martin assaulted him as a result of the approach? Martin was no altar boy. He had a track record of getting into fights in various situations. If Martin really did consider Zim a "creepy-ass cracker", is it possible that he would not have been receptive to Zim asking him what he was doing in the neighborhood?
I'm not sure that they are going to allow any info about Martin's previous history of fighting presented.
Is it strange that the girlfriend heard nothing as Martin and Zim confronted each other? No words exchanged between them before the phone went dead? And there is the fact that the phone was found in Martin's pocket ... not in his hand; not dropped on the ground. This might indicate that he had hung up the phone; put it in his pocket so his hands were free to confront Zim. This would not tell us whether Zim was moving toward Martin ... or the other way around.