Okay, what am I missing?

If there was a "fire" there would have been some evidence in the engine compartment, right? Melted plastic, charred paint, soot marks, whatever? Even if it was just a piece of road trash or a rodent nesting on the exhaust manifold, there would be SOMETHING left behind. Seems pretty black and white to me - if there was evidence, you had a fire. If no evidence, no fire.

In the case of the X5 that burned to the ground, I am guessing a loose connection sprayed fuel on the exhaust manifold. If that had happened to the OP, turning off the ignition wouldn't have made a darn bit of difference.

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2011 X5 35D Deep Sea Blue / Oyster
2008 M3 Vert Silverstone II / Black Novillo, 6MT
2008 X5 3.0 Platinum Bronze / Sand Beige Dakota
2007 X5 3.0 Space Gray / Gray Dakota (Retired)