In "The All-American Slurp," the narrator is awfully embarrassed when her family brought chairs to the buffet table, not knowing where to sit. But when their western neighbours attended their dinner party, she was shocked by their manners, and the way they trated food.
The author includes details about the dinner party hosted by the Lins to show that not knowing someone else's culture is not something to be ashamed of. It is normal to not be familiar with other people's customs, and people should be pacient and teach others rather than to get angry or offended.