How could Calista continue to call him a student at that stage? She had unknowingly started to treat Zavier like a peer or an equal after the incident with Kyouko and the other S rank mages. So, the reason that she had never felt odd calling Shiranui her best student was that she had never considered Zavier her student in the first place. He was too strong for that, almost like a cheat card.
However, before Calista could have called out to the referee in order to announce her forfeiture, someone else beat her to it. It was the white bearded old man let out a roar to attract the attention of the referee while waving his hand furiously.
The referee turned towards the old man in response to the roaring voice that was full of authority.
Calista was dumbfounded as she was just about to call the referee before she had been interrupted. Her words had been forcefully stopped in her mouth and she barely stopped herself from rushing towards the rude old man.