Most of the extra fuel was actually used(or not used actually) on the burnout. The average fuel car will use approx 6 gal of fuel during the burnout, back up and stage procedure. A malfunction in the fuel system may have allowed extra fuel to be sent through the barrel valve and into the motor, most of it unburned, and right out the headers on the burnout. A couple extra gallons pumped through and out the pipes would weigh 20 lbs. Im sure the Force cars are VERY close to minimum weight and that extra fuel that remains in the tank after a 1000 ft run can make all the difference.
It also sounded on the broadcast like there were some shavings or foreign debris found in the new cars fuels system after the run, either causing or contributing too the motors demise at the end of the run. The motor ran lean at the end, as is evidence of the unusual amount of death smoke out of the exahust (even for a Force car) at the end of the run.