Unless I've missed, it the report doesn't say that the student had already completed any rotary solo. In that case IMHO the student is not in a position to start the aircraft unsupervised (as per the ANO amendment).
Post first solo, I'd always be stood nearby so that if the student didn't follow instructions I could walk over if the RPM was increased above 70%. Accepting students need to start the aircraft solo to gain experience and confidence once I was satisfied that aim had been met, I'd explain that I'd like to sit with them purely to watch the start (I called it skills test preparation).
I also used to teach that students rolled the throttle slightly closed THEN raised the lever a little amount. If the horn didn't sound then roll the throttle closed a bit more. Battery on and engine off a student can be shown just how a small a collective up input is required to get the horn blaring.
Tricky one this as FI is technically the P1 unless the student is solo flying on that sortie. I used to be with my students well before they reached a flight RPM, afterall that's the time I was being paid for.