Hua Xiaoqing has prosopagnosia, which she doesn't think is serious, and she also has a character that can be described as free and easy or as big-hearted.
So she didn't know who the boy she was asking for money was when she got on the wrong bus and got on the bus again in the wilderness with no money. So she didn't know which boy she had met and had a great conversation with many times when she went to Fenghuang Ancient City. So she didn't know that the boy who was always praised by her roommates every time she rubbed shoulders on campus was the same guy.
But he met her again and again, at first inadvertently, but later in his heart.