NY explained on 23/07/2018 :
How would the sump oil find its way into the cylinder? Via leaky piston
rings? I presume top gear and hard on footbrake *should* stall the engine.

There are various ways for the engine oil to get into the combustion
chamber, there are numerous examples on Youtube of runaway diesel
engines. Some have even tried to use it as an excuse for speeding for
tens of miles. The footbrake certainly 'should' be able to stall the
engine, the engine will have much less power available than normal.