Boys rarely take the initiative to chat with me, but he will reply when I find him, and sometimes he will explain if he doesn't reply to the information in time. Why?

More polite to you, polite but not close. Simply put, he has no other thoughts about you, or he is afraid of your misunderstanding and deliberately keeps his distance from you. If you don't particularly like him, there is no need to spend too much thought on him. Of course, in order to avoid future regrets, you can also ask him what kind of girl he likes.