Looks like Autopilot was responsible for the sudden veering into the tree. So you have sudden odd behavior by AP along with an unstable battery that exploded upon the car mildly hitting a tree.
Again it looks like a battery short was in progress and that short led to AP glitching causing the accident. The impact against the tree allowed the overheating batteries to fully ignite engulfing thr car in flames. Ive strong suspected this is what happened in the Texas crash with autosteering taking control of the car despite AP not being enabled. The only way this could happen is likely via a short circuit sending the computer incorrect information.
As this accident occurred during a solar storm it seems that either electromagnetic circulation within the cars wiring or electromagnetic induced heating of the batteries led to the short.