According to employees familiar with the practice, Facebook has been hiring outside contractors to listen to and transcribe user audio. While Facebook claims the transcriptions were done to improve the voice-to-text transcription features of its Messenger app, the company's data use policy makes no mention of humans listening to or transcribing audio.
https://www.notebookcheck.net/Facebook-paid-human-contractors-to-listen-to-and-transcribe-audio-from-users.430330.0.html