I think that's the crux of it though, it doesn't answer the question. Fluency should be disregarded if the core function of the essay isn't met.
Im kind of in between both you guys. If an essay fails to address the question, it should not get higher than a band 4. However, I think fluency, grammar etc should be considered in the marking, although not to the same extent as answering the question. Also, 3/20 is ridiculously low - they dont even mark that hard on uni essays. I remember they showed us an anti-exemplar essay in uni which had all the essay writing mistakes in it. The lecturers told us that an essay like that would get around 35%.The marking criteria for a HSC course isn't just about answering the question. It's also about engagement with the texts, and showing that you can identify, analyse and synthesise techniques and their effect as well.
I'm not condoning writing a pre-prepared essay without consideration for the question, but 3/20 is overly harsh, and if I were to bet, would not abide with marking criteria. To me, it seems like said teacher is just trying to make a point about pre-prepared essays by punishing the student, rather than conforming with a stringent set of marking guidelines.