This isn't written on the page linked. Where are you finding this?

For other people who only read the comments and don't read source material:

"Turn on communication safety to help protect your child from viewing or sharing photos that contain nudity in the Messages app. If Messages detects that a child receives or is attempting to send this type of photo, Messages blurs the photo before it’s viewed on your child’s device and provides guidance and age-appropriate resources to help them make a safe choice, including contacting someone they trust if they choose.

Messages uses on-device machine learning to analyze image attachments and determine if a photo appears to contain nudity. The feature is designed so that Apple doesn’t get access to the photos."