Difference between WhatsApp audio and WhatsApp voice notes
The folder WhatsApp/Media/WhatsApp Audio/ contains the downloaded audio files that you received as an attachement from a contact. The file names usually start with AUD-.

The folder WhatsApp/Media/WhatsApp Voice Notes/ contains the voice files that you recorded using your Whatsapp. They usually start with filenames containing PTT- and stored under corresponding folders with date of the recording.