Who is New Korean schoolteacher from Lost Names: Scenes from a Korean Boyhood and what is their importance?

New Korean schoolteacher tells the boy about the Non-aggression Pact by his new map that the boy helped him hang one Sunday. He is uncertain what that means, and since the boy and his father are going to the bookstore, the teacher says he's going too. At lunch, grandmother warns her son to be careful because the teacher was sneaky as a boy. At the bookstore, the boy's father, teacher and store owner talked quietly about events. The store owner warned the teacher, whose eyes tear up, to keep his wits about him.