I agree, flat spin is really not an option here, the numbers barely fit with a spin at all, or even a stalled condition. If the autopilot stalled it, or it was passing in and out of a stalled condition with an incapacitated pilot holding it back, it would show a much shallower porpoising profile. As has already been discussed it looks more like something catastrophic happened that also caused an amount of drag that put the aircraft into a very steep, but restrained dive. Something more like a Stuka dive bomber, which was the only dive bomber capable of a sustained completely vertical dive, it even had an automatic dive recovery mechanism as pilots could black out from the g load during pull out.
Of course it goes without saying that having not had the experience myself doesn't rule it out of the realms of possibility, but I very much disagree it's a highly likely scenario.
I meant highly likely over the career of an instructor, not on a day to day basis. It will also depend on what types you fly, some are more aggressive in spin entry than others.