Hmmmmm. Far be it from me to pass judgement on others. However, what I will say is this: Surely, the job of an instructor/examiner is to provide a learning experience for (or assess) the student, while managing the risks associated with it?
In my mind, shutting off the fuel and causing the engine to actually stop (particularly in a single) is increasing the risk you are exposing yourself and your student to for how much extra training benefit??...
I won't say any more than that, as I wasn't there, but thought I would throw that thought in early!