SPOILER & LIL EXPLANATION AHEAD
the blond guy or yunjae is somewhat innocent after kid hajun was out of the hospital he immediately wanted to find kid candy/shihyeon, then he mistook kid yunjae for kid candy/shihyeon because he saw him crying and has a scar on his wrist and for this reason, before kid hajun was about to faint from the accident his only basis for kid candy/shihyeon was his wrist covered in blood, thus a misunderstanding happened. Since kid hajun believed that kid yunjae is kid candy/shihyeon kid hajun took photo with kid yunjae and that explains the photo we see in the manhwa.
men the twist got me so bad n i like it, i really love psychological stories, its so fcking messed up and i like it maybe i aint normal