I think they talked about this in the novel where they were thought as a part of the 100 families because of the 'shi'. Since more than one family there has 'shi' in their name.
MC: no I can't let her know who I am because I want to purcue magic peacefully.
Also MC: Shoots some amazing magic when fighting in front of the whole school.
Seeing how the examiner expected him to receive the attack made me think the world is JRPG or Chinese novel's world where avoiding attacks is for some reason is not possible
@JuliusCV, reading your comment made me really hate how the goddess doesn't make any sense. Looks like I will drop this if the next chapter does not clarify the logic behind her actions.