A boy I know, he went downstairs at the stairs, and I was going downstairs. He stood there for a while. After I went downstairs, he didn't go downstairs.

There are many such situations. First, it is possible that he suddenly remembered something and forgot it, so he turned and went back upstairs. Second, if there is anything between you, he may not want to see you. Third, he has a crush on you, but he was shy and nervous as soon as he saw you, so he ran back, so all these are possible. If you want to know, if you know him, you might as well ask him directly and guess. joke