To add another speculative angle, how long was the aircraft running on the ground or taxiing for departure? Maybe the fire was burning longer than we all think.
Again, pure speculation but would be interesting when the final chain of events is announced.
I try to take everything in when doing final checks on my side of the aircraft (exterior) before getting in, like am I taking everything in or just glancing it over. I would hope a fire would be readily detected but would depend on where it started I suppose.
Just one more thing to make you think about what you’re doing. At least I’m fairly confident primary structure in my airframe will last longer than a few minutes in the unfortunate case of fire, still rather not experience it!
FltMech