First University's Guardian Formation was a nested formation.
The campus walls, fences, and the like formed the boundaries of the inner formation, while Puji Island's winding coastline formed the outer formation. Simply put, the inner formation's protection was more meticulous and its security tighter; the outer formation was comparatively more relaxed—this was precisely why His Grace had chosen to "chat" with that government-sponsored student after he left campus.
Though Milton was getting on in years, he was not senile. He would never openly make trouble for their student right under the noses of a group of old wizards.
As the saying went, sneak quietly into the village; no shooting.
The outer formation was managed more loosely because, aside from the many students studying at First University, Puji Island was home to large numbers of merchants, adventurers, and even diplomats from other civilizations. They could not possibly remain obediently cooped up all year in a campus no bigger than the palm of a hand, burying themselves in their studies like First University students.
Therefore, for students enrolled at First University, only a few days during the winter and summer breaks, when the Guardian Formation was fully opened, offered them the chance to leave the island. Wizards from outside the school, meanwhile, could conditionally land on or leave one of the Wizarding World's most mysterious islands as long as they obtained an Invitation Letter or pass from First University.
It was somewhat like a school with strict access control. During class hours, the main gate remained tightly shut, opening only for that brief period after school to allow students in and out. The small gate beside it, or side entrance, was reserved for visitors entering and leaving the school—under normal procedures, every visitor would be repeatedly examined and cautioned by the gatekeeper,