???

In Korean “hyung” is something you call your actual brother. However, it can also be used with guys who are a little bit older than you but aren’t related to you. It’s like a symbol of how close your relationship is. Like “we’re so close to each other that we consider ourselves family”. It’s not that extreme but that’s the basic idea. Girls do it too. They call their crushes or boyfriends “oppa” partially because it’s cute and partially because it signifies the closeness of their relationship. “Oppa” is the word females use instead of “hyung”

Ik but he called him bro not hyung or oppa

In the translator notes, they said that Sangwoo said hyung

oh okay but thanks for explaining

But hyung and bro have different meanings. You can call anyone bro, regardless if there's an age difference or not. You can call a complete stranger bro. You can even call a woman bro.