Pure speculation, but here is a possible scenario, after all this is a rumour network...
Elevator trim tab failure at high speed causes extreme high 'g' pitch up, pilot blacks out, slumps forwards, 'g' causes tailwheel unlock, aircraft impacts at full power.
100 percent agreed, and the TT failure was the result of a high-speed stall and buffeting. To say the pilot is to blame is an understatement. The one thing you can't do at an airshow is crash into the crowd. That's just not allowed.
This Mustang was extensively modified but still a Mustang with short wings. It had aerodynamic limits based on being a Mustang. I think he forgot that.
Interestingly it's been rebuilt four times, once after being gutted (for parts?) and twice more for previous crashes, in addition to the radiator removal and cooling system modification. Not a happy airplane.
-drl