When I was tutoring algebra, I sometimes ran into students who could solve the problems in the book, but if I wrote a problem that looked a little different or that combined two of the concepts they'd supposedly learned, they would be lost. I gradually realized that they didn't understand the concepts at all, but had learned to follow patterns. ("When it's one fraction divided by another fraction, flip the second fraction over and multiply. Why? No idea, but I get an A.")

This feels like that: a "student" who can produce the right answers as long as you stick to a certain set of questions that he's already been trained on through repetition, but anything outside that set is hopeless, even if someone who understood that set could easily reason from it to the new question.