All I can say is that at 500 indicated mph, the aerodynamic pressures exacted on these craft are unlike just about any other vehicle. The P51 wasn’t designed for the continuous speeds (and aerodynamic pressures) typical at Reno. Those racebirds are besting the OEM (North American specs) speeds by at least 150 mph. At these pressures, the apparent loss of the elevator trim tab can indeed be the causative factor. Probably failure caused by high speed flutter. (For the uninitiated, think of a flag being whipped by a high speed wind).
This sad event probably means the suspension (and possible termination) of Reno races.