Who is to say that science is not advanced enough to fully say SHC is impossible? In another few decades we'll be laughing at current science.
There would be no evidence of spontaneous combustion. Your point is poor. It's like saying there's no evidence that a meal was cooked in a microwave. Yes, the result is cooking, but with many foods you can't really tell if something's been cooked with a microwave or boiled, etc.
The doctors looked for flammable gasses, but you don't need only flammable gasses for fire. If the baby had an imbalance of enzymes, and these enzymes were suddenly activated by a hormone and this produced lots of heat, then of course it would leave no flammable gasses - the end point would simply be heat.
Even if there was suddenly lots of a reactive chemical being produced by these enzymes which could've contributed to the heat when they reacted with the enzymes and other material, fat, etc , these chemicals are broken down once they react, so it'd leave no evidence.
Guess what? Thinking a little is good for you.
And I know it happened because I know what I experienced and my friend backed me up. You cannot tell me otherwise.