Yes the gel. From the faq on Homepage | FAQs it sounds like the stuff is pretty much made out of petroleum, seeing as it doesn’t mold or rot, supposedly is “inorganic” (but much cheaper than any silicone I’ve ever seen) and so forth.
So why shouldn’t it burn at appropriate temperatures or pressures? Besides that, after the flash, there’s a prodigious amount of smoke coming out of the entry hole, suggesting the flash was combustion. Additionally, the flash was orange, instead of white, suggesting it came from the combustion of organic molecules, and not a sonoluminescence flash which tend to be much closer to white or blue.
