The Skeptical Inquirer article I saw discussed the “shrunken skull”, and deduced the same thing. It wasn’t a shrunken skull, but merely resembled a shrunken skull.
As for SHC, I have seen a followup article in SI (and subsequently a program on, I believe, The Learning Channel) where some scientists (I forget who) actually performed an experiment demonstrating the method of SHC. They took a pig carcass (because pig flesh is very similar to human flesh) and wrapped it in cloth and placed it in a test chamber fixed up like a typical bedroom. The carcass was lying on some carpet, and had furniture, newspapers, a TV, etc all around similar to common descriptions of SHC scenes. They then ignited the cloth on the pig, and watched. Over the course of 8 hours, the pig slowly burned away via the so-called candle effect or wick effect. What happens is the clothing burns quickly, and creates enough heat to start the body burning. The flesh then melts the body fat, which pools into the surrounding material - carpet in this case, I believe, but typically an overstuffed chair, or a mattress, or just the clothing. This liquid body fat burns - not a 2000 deg F that crematoriums use (and only for 2 hours), but at about 800 deg F. This lower temperature prevents the fire from spreading, and the fire stays contained to the soaked fat. It thoroughly burned the bulk of the pig carcass, including some of the bones. The experiment was stopped before completely burning out because of time limitations, but it is clear the effect of the burn was the candle effect, and that it was consuming the entire carcass bones and all, and that it was not spreading to the furniture or newspaper or other flammable materials just inches away.
As for why a limb will often be left behind, the limbs have a lower fat content than the torso, and if protruding away from the torso can extinquish before the fire spreads. When the fat runs out, the fire burns itself out on the nearby consumables - the clothing or bedding, but is too low to spread.
During the experiment, they monitored the flame height and temperature. It was a stable fire that would not spread. That is why SHC cases are so different than typical fire experiences. Normally when you have a large fire in, say, a house or other building, it is big and quickly noticed and put out. Even when it isn’t stopped and burns itself out, the effect of the higher temperatures from the surrounding fire prevents the wick effect from establishing, so the fire burns out much faster than the 6 or 8 or 10 hours needed to fully consume the body. That’s why crematorium fires don’t completely consume the bones - they don’t run long enough. The trick is that SHC cases involve small fires that don’t spread so they are not noticed, and thus allowed to burn for hours on end.
See, nothing mystical. Bizarre, gruesome, fascinating, but not mystical.