"After he pushed the stick FULLY forward and our cessna 150 went from about 45 deg pitch up to almost vertically pitch down."
Had almost the identical situation happen to me. First flight with an older guy brushing up for a PPL skills test after 5 years of a lapsed PPL. The student flew extremely well and his handling was confident, so I asked him if he'd be happy to show me a clean stall recovery. Without prompting he did a full hasell check and slowed the a/c down keeping it rock solid level, leaving me relaxed and calm, and then at the first pip of the warner the stick went hard full forward. My note pad actually 'shot' off of my lap and firmly pinned itself to the roof lining while I struggled to push one hand hard on the roof so that I could hold myself down enough to reach the stick........ 'Errrr I have control'
As my CFI always states, 'it'll be the guy with a license who tries to kill you, not a new student!' never relax your guard.
Was left wondering about the structural implications of high -ve G in a 9000 hour C172!