Luckily for Johannes, The Doctor couldn't read minds. Not without a connection at least. Nor did he intend to. But if he could have, Johannes would have found himself very quickly out of the class, or at the least, the field trips.

He more than discouraged changes in time, especially for personal gain. Established timeline events must not be altered. He spent a large portion of his lifetimes stopping people from doing that very same thing.

Oblivious to Cabal's reasoning, The Doctor acknowledged his profession with interest. before carrying on with the class. Maybe he would go to that carnival later.