Nothing in that quote backs up your statement.

Tim Cook is describing how encryption works - he is not saying that the Chinese government doesn't have access to the data at rest with the iCloud encryption keys. Amnesty International [1] sums it up:

>“By handing over its China iCloud service to a local company without sufficient safeguards, the Chinese authorities now have potentially unfettered access to all Apple’s Chinese customers’ iCloud data. Apple knows it, yet has not warned its customers in China of the risks.”

They raised this issue three full months before the Chinese government went ahead and nationalized all of the Apple user data and encryption keys.

[1] https://www.amnesty.org/en/latest/news/2018/03/apple-privacy...