The waitress, who has a Korean accent, says that Daniel needs to teach his girlfriend to use chopsticks. She explains that her son dated a white girl, and her husband didn't accept it. They didn't speak to their son for a year, thinking he'd finally see reason. He didn't, and now she misses him. When he finally called, it was to invite them to his wedding. Her husband said no, and finally, her son stopped begging. The waitress saw pictures of the wedding on Facebook, and saw photos of her son's son and then his daughter as well. Now, when Korean boys come into the restaurant with white girls, she gets angry. America tries to take everything from immigrants.
The waitress's husband believes that being Korean in South Korea and in the US should be one and the same. Remember Natasha's comment about the US not truly being a melting pot; the waitress's story is clear evidence that Natasha was right. This shows that for some immigrants, becoming connected with their new country isn't actually the goal. The waitress and her husband expected their son to exclusively date Korean girls, thereby rejecting the idea of a melting pot.