Well the part about the old man contains irony: he claimed to have no appetite, but his action of finishing five bowls of food is the opposite of what he said.
The implication is that someone who says he has no appetite might typically eat five bowls of rice because of the norms of eating a large amount of food in Korea. Whether it's true or whatever, who knows, but that's what's being implied and illustrated in this example.
Well the part about the old man contains irony: he claimed to have no appetite, but his action of finishing five bowls of food is the opposite of what he said.
The implication is that someone who says he has no appetite might typically eat five bowls of rice because of the norms of eating a large amount of food in Korea. Whether it's true or whatever, who knows, but that's what's being implied and illustrated in this example.