The final report has the important picture... The seatback was scorched, as was the canopy. Batteries were ejected during impact sequence, so this wasn't post crash damage.
So the pilot had 500celcius/923f on his back after the 'thermal event' started. We know how hot a small glider cockpit can get just in the sun - add crazy heat source + blinding (lipo fires are nasty, its like tear gas for your eyes/lungs) smoke. The pilot was basically along for the ride as soon as those packs lit off based on the scorching + add in some melting/burning composites.
skip to a minute in for the poof.
I think speedboat is probably referring to a previous comment I made on a previous electric thread. Discussing this with my local fire captains - they'd prefer a wildland fire + separate off airport landing site vs a fatal plane crash/fire. May slightly differ if you're operating over dense urban areas. But it's a big earth - the likelihood is a burning pack separating and injuring others is up there with the risk of someone being struck by a re-entering satellite.
California/USA legal issues is a whole different can o worms.