it shouldn't really matter if you have proper limb control as the restraint should restrain you no matter what. lets say a person becomes unconscious on a ride. they'll loose control over their limbs, but you would expect they they would stay in the car (albiet flopping around) if the restraints worked properly.
at this point, I don't believe that the cause of the accident is known so blaming either the rider, ride operator, or ride manfacturer is permature. wait until the reports are released to point the finger.