I don't really think so because it means that Daiki had been lying this entire time to Minjun
not saying something about yourself doesn't equal lying
it's a lie of omission, and Daiki has said that he doesn't understand Minjun when he speaks korean so it is a lie.
I don't think he's overreacting, this guy has been saying things in Korean thinking daiki doesn't know and the fact that he knew, I'll just be mad and embarrassed
I think minjun is overreacting a bit