Comment by Stranger on Baits - Chapter 22

@Stranger No, its right that way, Hyung is for older brothers and Sunbae can be used for older and Younger ones. It's for if a person is more experienced in a field like school or else, like better at it or longer working in the field.
Bc Ml skipped some classes and became top of the class he's more experienced and the sunbae.
I hope that explains it, look it up in the Internet If not.