From the description of events, it seems more likely that the thermal runaway already started. The CPU detected the critical heat and shut off, as it is designe

From the description of events, it seems more likely that the thermal runaway already started. The CPU detected the critical heat and shut off, as it is designed to do to protect THE CPU from damage. The problem is that it wasn't the CPU creating the heat, but the battery. Turning the device back on likely had nothing to do with the problem. I think this comes from a lack of understanding about how the problem started. Yes, excessive heat CAN cause a critical battery condition, but this seems unlikely, as the batteries should be designed to handle much more heat than the CPU can generate. Rather, I think the batteries caused the heat, not the other way around.