Yeah, Heejae was and still is a bad teacher. His intentions were never purely about music in the first place. His whole “looking for a gem” mission was basically driven by escapism, personal obsession, regret, and grief. He never gaf about those kids, they were disposable, deep down he was just looking for something to fill the void in his miserable life and used those students as tools.
I don’t think you understood me, I meant like outside the context of the story. I understand he’s presented as one of those abusive teachers that tries pushing their students to be better (obviously its not as successful as he wants to believe it is), I think he’s a really interesting character! I’m just saying it’s really silly when he says stuff like Garam having natural legato, which means basically nothing in the real world. I’m not criticizing the story I really like it!
Well then i guess it could be the authors knowledge of musical terminology, could be something missing in translation, could also be intentional choices to reflect his character as someone who somehow ended up as a uni professor without any sort of teaching qualifications or human qualifications, for that matter. We’ll never know i guess lol

This is more of a personal thing but as someone who went to school for music Heejae is such a bad teacher. Like ignoring all the abuse none of the things he teaches are really that useful. I’m guessing this comes from the author not being a musician, but damn its hard to take it seriously when he’s always just saying some bullshit or the most obvious thing ever.