Its not the root cause, but it seems that the aircraft hit the runway with a high rate of descent. This pushed the main landing gear upwards through the wing and released fuel, which caught fire on the next bounce.
The root cause is being given as a lightning strike but that may not tell the full story. Part of the issue is that the aircraft was flying on direct law (full manual control) and the crew weren’t prepared to land it in that condition. They may also have been missing control of some control surfaces, because of an electrical failure.
