I hesitate to suggest it was the result of the kind of ham-fisted handling technique that might be ignored by Cessna's relatively benign and customer friendly aerodynamics
That is pretty seriously uncalled for and frankly a dumb remark - there's really no point in trying to score points about what a superior pilot you are to those who habitually fly other kinds of aircraft (in my case, including Pitts S2C and Robinson 44, as well as my own Cessna).
As I pointed out in the OP, we were intentionally exploring the deep stall regime, to observe that airflow doesn't reattach at the same AoA it detached at. With any reasonably sensitive handling, of course this won't happen. It's just an interesting observation about aerodynamics.
As for the airspeeds, we certainly weren't on alternate static. This is an extremely well maintained aircraft, and the person I was flying with has a lot more advanced experience than you do, I'd be willing to bet, including U2s and a long stint as a USAF Instructor Pilot. (Preparing now of course for inbound about well what do you expect from those uncouth Americans). Incidentally the 260 is his favourite aircraft, and the one he says he will keep if/when he retires from the flight school business. I rather like it too, though I'm very happy with my TR182.
I remember now why I'm reluctant to post anything serious on this forum...