and was testing the Cessna’s aft center-of-gravity stall characteristics
Two thoughts come to my mind with that information: If there had been a ballasting error, and the C of G was actually further aft than intended, recovery could have been an extra challenge. If the stall was allowed to develop into a spin (which may be inferred from the final very tight turn in the ADS-B trace), recovery would be demanding. If both factors were combined, it would be a great challenge for the pilots to recover.
I am responsible for not detecting a couple of ballasting errors during flight testing over the years, which has made me extra vigilant in that regard. I errantly accepted a "behind the aft limit" Cessna 185 for spin testing once, and it was immediately apparent that spin recovery was noticeably more difficult behind the aft C of G limit. Lesson learned!