As others have said, it should be opt-in, not opt-out, if they are going to do it at all.
Just out if curiosity I’d like to know how they can be sure supposedly ‘anonymised’ recordings contain no personally-identifying data before humans hear them?! If that could be so assured, why do humans need to listen at all? It sounds paradoxical to me... like, they listening to improve accuracy, but claiming before the audio gets to those people they do something that would require an excellent level of accuracy... huh?!![]()
It anonymises the recordings so they aren't linked to your iCloud account, but if you literally say "hello I'm John Appleseed from Cupertino" then there's not really much anyone can do to protect your identity.