A similar thing happened to an ex-QHI colleague of mine. The pre-brief went along the following lines, as per the SOP:
Student was to handle the throttle whilst the QHI flew the aircraft throughout. The run in was at 120 kts and 200 ft agl (might have been lower, it was a very long time ago). The aircraft was to be "zoom" climbed and a variable flare EOL carried out to the airfield (again Tern Hill).
Commands from the QHI were to be: "Identify the throttle" (student to reach up and to place hand on throttle, situated on overhead panel).
Then QHI: "On my command, 3-2-1 NOW!" (On NOW! the student was to fully retard the throttle).
What happened was: "Identify the throttle" - Student reaches up, grabs throttle and retards it!
Gazelle incapable of reaching airfield....but thankfully it was a safe, albeit embarrassing, landing in the adjacent farm field.