Well for one thing he was the commander of the watchteam there....and his job in the neighborhood was to “watch”. He was doing so while on an errand.
Zimmerman’s carrying was perfectly legal. There’s no evidence he was doing more then finding out what the guy was doing there. Many would have done the same thing when a rash of robberies had been occurring.....and why they determined to have a Watch Group.
Carrying a gun does not mean one is intent on using it....in fact most gun owners I know see that as a very last resort.
Furthermore it was not unitl Zimmermans cries for help brought no relief that the gun became an issue.