If the computer detects a malfunction in the BAS/ESP system it will automatically deploy the rear wing as a default safety feature. The wing deploys for the sake of high-speed stability, if the car has ANY problems with the stability programming there's automatic deployment of the wing to offset any future liability issues because people love to sue car companies.

It's much the same as the drive-by-wire throttles in our cars........if there's a problem with that circuit the throttle will default to OFF. I'm betting Toyota wishes they had done the same thing in their cars.