A fire is indicative of a short.
What shorted is unknown. Even the exposed bullet plugs of an ESC can cause such a thing on ANY airplane, if they remain in contact with one another.
Of course you could have just had a bad ESC.
If this has never happened to others, you haven't been in this hobby long enough!
Anyway PM John...
Because it happened with one plane, does it in any way indicate the same thing will happen with another.