Isn't Bong Won mostly upset because his "son" is leaving home? Plus the old lady younger sister is going away. He must be feeling like everyone's leaving.
Although, what with her being all old and going away, and that kid's rude question, under there somewhere he might be wondering about dating a girl who's not a vampire and is going to grow old and die. It's like the old elf-human problem, only with a potential solution . . . but it's the kind of solution that it's sort of awkward to bring up.