Poonpossum,
It's quite simply explained really.
If you have been flying for a few hours with the landing gear retracted and suddenly, when the temperatures around the brakes are about -40C, there is an indication of heat, there are two potential causes. It's either a fire in the wheel-well (lots of electrical circuits, hydraulic systems at high pressure etc down there) or it's a faulty brake temperature sensor.
With no way of telling for sure......what would you do with Manila as the nearest airport?