Where does Tim Cook specifically say that? What you quoted does not support that.
The encryption keys are for iCloud backups at rest, for which a copy of the keys are stored serverside. This can decrypt all iCloud data, including messages, pics, videos, documents, etc. Tim only described E2E message encryption between users, not encrypted iCloud backups.
Again, Tim isn't saying what you think he's saying. He's intentionally not answering that question or misdirecting - he's doing it all over again here:
The encryption keys are for iCloud backups at rest, for which a copy of the keys are stored serverside. This can decrypt all iCloud data, including messages, pics, videos, documents, etc. Tim only described E2E message encryption between users, not encrypted iCloud backups.
Again, Tim isn't saying what you think he's saying. He's intentionally not answering that question or misdirecting - he's doing it all over again here:
https://news.ycombinator.com/item?id=21218529