It seems you haven't read the whole thing.
Torres and Norton were found guilty of threatening to kill some of those attending the child's party while shouting racial slurs at children.
Torres was said to have been carrying a shotgun, according to prosecutors. He was sentenced for aggravated assault with a deadly weapon and for violating Georgia's street gang and terrorism prevention laws.
They weren't sentenced for the flag or for simply carrying a weapon. They were sentenced for attacking some people at their party, which I assume was taking place on private grounds. You can carry a weapon openly, but entering a private property with a gun and threatening the owners might be taken as an assault with a weapon.
We don't know exactly what they did, because the article is written in a way that suggests they were sentenced for driving their car with a confederate flag and for carrying a weapon, but it must have been more to that.
That's the thing, they didn't enter private property. They and some other people doing the same thing drove their cars past the party yelling racial slurs.
"They are part of a group of at least 15 people charged over the incident in which cars were driven along the street flying the Confederate battle flag in Douglasville, west of Atlanta, in July 2015."
"Torres and Norton were found guilty of threatening to kill some of those attending the child's party while shouting racial slurs at children."
"Residents at the time told local media that the people in the vehicles were shouting racial slurs, but the group said they were attacked."
See, they didn't get out of their vehicles. The firearms were on their possession in the car. They just drove past yelling racial slurs, like that hasn't happened a billion times before.
I think what were seeing here is a example being made of these two so no one else incites hatred. The sentences are way too long for what they did. Maybe 2 years max, even that's too much.