Quite possibly the fuel simply leaked while in a slipstream environment and wetted a lot of surfaces behind the nacelle in flight before dripping down and wetting the nacelle and the ground after it stopped and only then the ignition.
Lomapaseo, I can completely see that theory working on the ground. Reports of kerosene smells in the cabin in flight seems rather odd considering the architecture of the engine and bleed system. It is a puzzle.
Perhaps the early reports of an 'oil pressure' problem precipitating the landing were wrong and it was in fact fuel pressure and the engine was not shut down.