Service with the Georgia State Guards was voluntary, but officers and men had to be exempt from Confederate service. It seems that the man in question had a discharge from regular military service. Company officers sometimes competed against one another to get enough names on roll, so it's not unusual to find the same man's name on different rolls.
We don't know why this man refused to be mustered, but any number of reasons are possible. Maybe at the last moment he just changed his mind and decided not to join.