> it's possible he had the laptop resting on some blankets
IIRC, Macbooks do not have vents on the bottom to be blocked in that way. The only vents on mine are on the hinge between the screen and the body, and the mechanism works so that the could really only be blocked from the top.
In my experience, resting a Macbook on something that's soft (like a blanket) so that the underside is blocked has rather catastrophic effects on its ventilation.
That said, it should not be possible to cause a runaway failure in the battery via the laptop overheating.
IIRC, Macbooks do not have vents on the bottom to be blocked in that way. The only vents on mine are on the hinge between the screen and the body, and the mechanism works so that the could really only be blocked from the top.