[Shooter 2.5]

My guess is that it was some stupid cavalryman (infantry don't carry pistols--and they weren't close enough for a Confederate officer to have done it),

The reenacters are saying the shot came from the confederate infantry side.

[Virginia Ridgerunner]

Officer then? Unless, it was one of those stupid local “shoot-out” events where the Confederate reenactors think they are Josey Wales. I’ve seem my share of those too, and have walked away.