To avoid giving out any false clues.. the Operator is not literally speaking French here. What you are seeing is a translation into English from the Mansionverse language the characters are actually speaking. And.. in the case of the phrase he used in that language, the best translation into modern English, the phrase that closest catches his exact meaning and intent, happens to be not "Goodbye" or even "See you later" but the stolen-from-the-French "Au Revoir." Just in case you were curious.