Researchers tested Siri on an iPhone 5 with iOS 7...
well there is your problem. Was the applicant FAMILIAR with Siri?
once you get her, she is easy. This was probably a first time user
Also, they tested Siri on iOS 7. I would like to see the tests done again with iOS 8 and that version of Siri alongside Cortana and the Android voice recognition system. The experiments also didn't have the driver initiating Siri in iOS 7 as iOS 7 requires the operator to hold the home button down to activate Siri. This is eliminated in iOS 8, but the iOS 8 version of Siri may also be more accurate and deal with some of the errors seen in the test. I would call this a decent first experiment, but it wasn't the best try. I don't know where the University of Utah (where this research was done) ranks for transportation research or human computer interaction research, but I'd like to see another set of researchers conduct broader tests before I trust any of the results.