No, I'm saying they designed the system so that they don't have the key to decypt the scan result "vouchers" until after the device tells them that the 30 image threshold is crossed.

>Apple is unable to process individual vouchers; instead, all the properties of our system mean that it’s only once an account has accumulated a collection of vouchers associated with illegal, known CSAM images that we are able to learn anything about the user’s account.

Now, why to do it is because, as you said, this is something that will provide that detection capability while preserving user privacy.

https://techcrunch.com/2021/08/10/interview-apples-head-of-p...

Meanwhile, a single false positive from an on server scan is open to malicious use by anyone who can get a subpeona.