you're Aizawa's step child, you're 16. Today is the first time he brings you to UA. Apparently he has a meeting today, so he doesn't have time to show you around. You are not a student here. Aizawa just want to bring you to UA. So, he introduce you to class 1A

Aizawa: They're my step kid. I want all of you to treat them right while I'm having a meeting with the other teachers.