Combination of hight COM, liftoff oversteer and (probably unintentional) scandinavian flick.

Biggest problem with pre-2015 mustangs is live-axle rear suspenshion. Driveshaft torque creates uneven weight on rear tyres, so when full throttle meats limited-slip diff car just do not want to go in a straight line.

Petroleum fly spends its larval stage within the tar pits, maybe its them?