I am making a guess he is referencing this: https://www.backblaze.com/blog/apfs-apple-file-system/
"Apple’s current encryption scheme is called FileVault. FileVault is “whole disk” encryption. You turn it on, and your Mac encrypts your hard drive. That encrypted data is, for all intents and purposes, unrecognizable unless you enter a password or key to unlock it.
The problem is that FileVault is either on or off, and it’s on or off for the whole volume. So once you’ve unlocked it, your data is potentially vulnerable. APFS still supports full disk encryption, but it can also encrypt individual files and metadata, with single or multi-key support. That provides additional security for your most sensitive data."
or this: http://www.pcmag.com/article/345519/what-macos-sierras-new-apfs-file-system-means-to-you
"APFS uses integrated encryption instead of the essentially tacked-on encryption technique used by the existing OS X FileVault feature that slowly encrypts or decrypts an entire drive. APFS can encrypt whole disks and individual files with separate keys for the file and its metadata, giving granular control that could, for example, let individual users modify the data in a file without access to a separately encrypted audit trail of the changes."
