@BL lover
not necessarily. It's used to someone you're very VERY close with, not just a brother. Its a sign of respect for someone older but it can also double as a sign of affection compared to Sunbaenim, which is more formal and used for someone distant to you. In Korea, they put a lot of strict distinctions on these things so getting called "hyung" isnt a light thing.
its basically the equivalent of "oppa"/"noona" for het couples. Calling your s/o "oppa"/"noona" when theyre older than you doesnt mean they're literally your brother/sister. Its a term of endearment.