Being willing to answer this question means he acknowledges Lan Jie.
If it were someone else asking such a question, Qiao Yu would probably ignore them. If pushed, he'd just retort, "None of your damn business."
The main reason Qiao Yu thinks that purely good people in this world are worth treasuring is simply because he hasn't met many that pure.
Most others are just good on the surface, and their most commendable acts are often at someone else's expense.
But Lan Jie is different. He's truly willing to give of himself, and he does it with genuine sincerity, not seeking fame or profit, and certainly not talking about it everywhere.
Even when two dimwitted students were having only buns for dinner, he would help. He even handed out two hundred bucks, and who knows if those two guys, Lu Jia and Ma Yufei, have paid him back. Qiao Yu figured that with Teacher Lan's nature, he probably doesn't even remember.
