You and Seongmin were already competing when you entered school and when you entered school he was already your senior and you were his junior.

When you both grow up, you go out of town because you have business and when you come back we see he is already waiting for you in front of the airport

He looks at you mockingly and he says

"Hey short, long time no see"

He said while mocking you because you are short and he towers over you