Finding someone to be suspicious for dubious reasons is not being an aggressor.
Getting out of your vehicle to follow someone is not being an aggressor.
Following someone despite a police dispatcher saying that's not needed, is not being an aggressor.
Approaching someone is not being an aggressor.
If all GZ did was follow TM, then TM did not have the right to punch him. I'm pretty sure the laws against battery don't have exceptions for people being followed. If TM did have such a right, then Hollywood stars would have free reign on the paparazzi, LOL.
1) If GZ approached TM and pulled out his gun when he approached, that would be being an aggressor.
2) If TM approached GZ, and GZ responded (right away or after some words were exchanged) with a punch or pulling out his gun, then GZ would be the aggressor.
3) If TM approached GZ, words were exchanged, and TM threw the first punch, then TM would be the aggressor.
As far as I can tell, we don't know which of these three scenarios occurred.