Every other participant on the stage was all supposed to have better bloodlines than Gustav so it came off as suspicious to the principal when he noticed that Gustav was surpassing them in speed.
'Maybe it's because of her,' Principal Erwin remembered that Gustav had been receiving training from miss Aimee.
It wasn't a secret anymore that Gustav was receiving training from miss Aimee but no one knew that Gustav's increase in strength didn't totally come from her.
Principal Erwin felt that Gustav's training with miss Aimee was the only possible explanation even though it was supposed to be impossible to train an F-grade mixed-blood to be more powerful than those that had higher grades. This was the explanation he came up with but that didn't mean his suspicion towards Gustav had reduced instead he knew that there was nothing he could do about it.