I was thinking the exact same.
it gets brought up later in chapters 105 and 106 in korean. the teacher is hus homeroom teacher, we've seen him quite a lot in the manhwa, he's not a bad guy. we don't know what they've talked abt but they've been meeting to talk like this a lot recently and i think he's trying to help him, talk with him, because he's worried. u can see that he noticed something is off abt him and he noticed it before in chapter 90 too, when cirrus told him that he prefers being at school than at home
Ooh, Ok, I got you ! Thank you for the brief recap, completely forgot about him
Wait Who’s the teacher that pulled Cirrus aside again? I feel like that interaction doesn’t get brought up after this, a bit worrying.