Stikes me as they must be using some pretty low melting point monkey metal for the inter-rotor finned bit!
Lets face it, the heat into your brakes comes from exactly two sources:
1) your legs – cycle along at the max speed you can manage with your brakes on, and if you’re speed is constant, all you leg power is going into heat in the discs – for most cyclists i can’t believe this could be more than ~200W for any period of time
2) Potential energy for height loss. The mass of you and your bike, from the top of a mountain to the bottom of the mountain. If you start at zero mph, and finish at zero mph, then all that potential energy has gone into your discs. The average “power” of course, depends on how short a time it takes you to get from top to bottom!
In each case, these energies and powers seem totally obvious and estimable!. To blame it on a “stone” in the disc is ridiculous, as that doesn’t change the energy being imparted to the disc……