Soju's poem is only three lines long, but it hides a small twist inside its title word. The speaker meets someone they call "interesting," and we expect a description of a fascinating personality. Instead, the only thing we learn about him is that he is sad, and the reason is that nobody seems interested in being his lover.
That repetition of "interest" is where the poem gets its quiet sting. The man is interesting, yet no one is interested in him. The speaker notices the gap between what he is and how he is treated. The tone is flat and matter-of-fact, with no dramatic complaint, which makes the sadness feel more real.
The speaker's own feelings are left open. There may be sympathy, curiosity, or even a hint of loneliness that mirrors his. The mood is gentle, wistful, and a little puzzled, as if the speaker is still wondering why this should be.