Well I'm glad the pilot is ok, but curious if there is a lesson I should learn here. Given a good distance from anything else hard, this doesn't seem like it should result in an unscheduled disassembly.

If you are thermaling, the glider is not operating anywhere near a structural limit like any max G or speed. Flying an inattentive slow circle makes for the stall and subsequent spin. (Ask me how I know.)

So why not just fly out of the unusual attitude? Was there another glider, or not enough distance to the ground? Or perhaps there was a problem with the recovery?

The NTSB seems to say that a stall spin should result in a broken glider. This doesn't seem right unless there is no other margin.