Istredd is never careless with his magic. It's the opposite, he is extremely careful and precise. He doesn't do any spell without being certain he has it under control. That came from his intensive training where it was clear if they got even the slightest thing wrong, a master mage could die. He would rather someone be skittish about their magic than arrogant and reckless.

He shakes his head and gestures for Wilhelm to sit back down. "We don't need to go into another room for mental magic. It's in the mind." No matter where they are it is the same amount of focus. They make the new room for fire so Wilhelm doesn't have to worry about burning it down.

Instead Istredd moves his chair so it is more directly near Wilhelm, they probably need to get more physically close, that's the difference. "I need you to trust me, because I need to go in and see where your gaps are before making an assessment. You have to allow me access." Technically he could just slam his way in, Wilhelm has no defenses, but he wouldn't do that.