I do believe I may have been that very student, much water has passed under the bridge since then
Even now as an R22 Instructor with many thousands of teaching hours I recount that story to all of my new instructors for 3 reasons;
1) Beware of students you havent trained yourself, they will do things you dont expect when you least expect it.
2) Do the right thing!! If you screw up, someones life can depend upon your integrity as a Flight Instructor. My Instructor's professionalism and subsequent actions / reaction (both to me and the company) to that incident were formative in my flying career.
3)Always fully brief a student prior to flight about low RPM recovery and autoration power recoveries so you are both on the same page and one of you isnt winding on the throttle whilst the other is pulling an armpit full of collective - sure fire power on overspeed. It is the instructor's job to prevent this happening NOT the student.
Geoff