Mustard,
How would you conduct a rapid precautionary disembarkation in this scenario exactly? Are you really suggesting that with fumes in the cabin the crew should have stopped, deployed the forward airstair and evacuated the entire a/c down these steps onto the runway? Or maybe they should have taxied onto stand and requested the handlers to bring steps?
A precautionary rapid evacuation is only really an option when the a/c is already on stand, with either steps deployed/attached or with an airbridge attached.