I reported the following. Would appreciate a comment from native speakers. "I'm not sure, but the pronunciation of "zone" on the audio sounds to me like there's a diphthong (long /o/ + schewa) rather than a pure long /o/?? Maybe the French do use a diphthong here??"
Although I am not a native French speaker, I do not here a diphthong at all. French does not use diphthongs frequently; I cannot even think of an example of one right off the bat. Perhaps you are hearing the nasalization of the oncoming « n »?