Haha it's actually 'Hyung'- it's polite in S. Korea to refer to an older person if you're a man as 'Hyung'.
When he was referring to him as 'Mister' he was probably calling him Ajusshi:
https://www.urbandictionary.com/define.php?term=ajusshi.
I had to remind myself as well haha.
*An older male.
Oh, that makes sense!
lol ikr made me feel weird but i just kept re reading it as "Luke hyung" instead and that made it better.
I'm just glad they made that change before having sex like in My Suha, Suha still calls out "Director" during sex so it could be worse
WHY'D HE HAVE TO SAY BROTHER THOUGH-