“People around the world could relate to the polarization it describes,” said Huh Eun, a retired college professor in Seoul and a fan of Mr. Bong’s films. “The film was an extended metaphor for how the deepening rich-poor gap in advanced capitalist societies breeds blind hatred and crimes.”

In the movie, a poor family living in a stifling semi-basement home uses subterfuge to get various jobs from — and feed off — a rich family in Seoul. Hence the movie’s name.

The film touched nerves among South Koreans because of its depiction of the squalor and exorbitant housing prices the poor face in the country’s congested capital city, and the deepening fatalism among the have-nots over their inability to climb the social ladder.

The gap and alienation between the so-called gold spoon and dirt spoon fueled a recent scandal involving the country’s justice minister, who was accused of using his influence to help his children get into prestigious colleges. The minister, Cho Kuk, resigned after weeks of public uproar, and President Moon Jae-in apologized to young South Koreans over the country’s growing economic inequality.

Mr. Bong’s film proves that a story that examines the struggles of ordinary South Koreans could strike a chord around the world because of the inequalities that afflict many societies.

“Miracle!” Woosang Lee, a Korean in Vancouver, Canada, wrote on Twitter. “I am happy and proud to be Korean. I have never imagined that this kind of thing would come.”

Another Twitter user said it “feels surreal to see a movie in your first language earn this much prestige from a Western audience.”