Just curious why did this interaction make you mad? If an painting student does nothing but paints eyes, that student will become really good at painting eyes. If a music student plays one song, they will get really good at playing one song. I've been in acting classes where teachers have had similar reactions, telling me and other students to not treat a scene like this or that. I took no offense to it personally and found that it helped me in the long run. That is not to say that the teacher couldn't have taken a moment and said "That was very good, it was good because you knew it so well, so lets not do that again" but I do not see the purpose in getting angry at such a phrase (except of course in the history of the Julliard program that Jacobs lays out here).