Yes, that’s the successor document. You can also use the old iPhone 4 era iOS security guide, the file system details are not a fast moving target. The addition of the Secure Enclave changes things a bit.

Anyway, the idea is that data only hits disk encrypted with a per-file key that is stored with the directory information. When you delete a file, the key is obliterated, rendering the deleted data unrecoverable from block storage. The explanation proffered by the journalist that data isn’t really deleted when you delete it from disk, doesn’t hold. Because it is. Or at least the key to it.

A more likely explanation is spare copies either in the cloud or on the device not getting cleaned up. But deleted files on iOS are proper gone.