In the interview, Craig discusses this. They did not previously scan iCloud photos because they consider it too invasive. They consider this less invasive, beca

In the interview, Craig discusses this. They did not previously scan iCloud photos because they consider it too invasive. They consider this less invasive, because Apple does not look at the content of your photo, except on the device. So the change was from "not scanned" to "scanned before upload on device".