What you describe in your last paragraph is NOT what happened to cause the fracturing. IT was not from simply wearing out. It was extreme friction over a short period of time that took the temperature to 1100 degrees. No normal wear condition will EVER take it to that kind of temperature.
When that video was taken, the damage had long ago been done. Read what he says about that.Actually, the hydraulics are not in play in the video. Clutch pressure comes from the mechanical finger springs. Hydraulics are only used to open the clutch when changing gears.
And yes, a worn out clutch slipping while in gear can generate some pretty intense heat. Normal clutches generate enough smoke and smell to inform the operator that something is not right