The spell that had been used by Aurora was a combination spell. It was something that not many mages knew about until later in life due to how dangerous they could be. Use the wrong amount of magic or wrong spells, and the effects could be disastrous.
With Raze being who he was, he had noticed it straight away. The way she was acting, the way the other student wanted to win, and what tipped him off the most was the look in her eye. He had seen that look before on others.
The bloodlust that they were able to feel in the hallway, it had to be from her, and she was going to act on it, by using a spell that would kill the others. In the situation they were in, she could claim it was an accident.
How was she meant to know that the combination of those spells would cause things to act like that? Which was why Raze was quick to act. He moved from his seat, and the barrier was the first problem.