Calpurnia's attitude is somewhat morally superior. He language becomes what Lee calls "erratic" but I think what Scout hears is Cal's language she usually uses with black folk. Cal is comfortable in doling out the appropriate punishment for Scout when Scout criticizes Walter Cunningham. We hear her comfort with being morally superior in these words:
“There’s some folks who don’t eat like us,” she whispered fiercely, “but you ain’t called on to contradict ‘em at the table when they don’t. That boy’s yo’ comp’ny and if he wants to eat up the table cloth you let him, you hear?”
“He ain’t company, Cal, he’s just a Cunningham-”
“Hush your mouth! Don’t matter who they are, anybody sets foot in this house’s yo‘ comp’ny, and don’t you let me catch you remarkin’ on their ways like you was so high and mighty! Yo‘ folks might be better’n the Cunninghams but it don’t count for nothin’ the way you’re disgracin‘ ’em—if you can’t act fit to eat at the table you can just set here and eat in the kitchen!”
Phew! That's quite a talking to! You can see that the punishment Cal gives is removing bad behavior from the rest of the group.
Scout of course is humiliated, but that's what happens when you are rude. This is the greatest instance in which we see Cal's attitude contributing to others. It punishes Scout, and gives human dignity to Walter Cunningham.