Thinking about it, it is perhaps a kind of ironic karma. If you remember how the blue-haired guy got close with Dan-i at the start, he became comfortable around Dan-i exactly because she showed no interest in him. I think he kinda hurt her feeling then at least a little too when he said that he liked her, but as a friend, because she was not interested in him.
And now it is exactly this quality of Dan-i that is going to torment him.
And is it significant that the white-haired guy could smell cigarette while talking on the balcony? Like, is someone listening in on them, or is it just a throwaway line to show someone in their room smoke?