Short answer: For ordinary content-policy reports, the reporter's identity is kept private from the reported creator. Copyright notices follow a separate DMCA process: the creator receives the substantive content of the notice, with the notifier's residential contact details redacted where appropriate. Do not assume a DMCA notice is anonymous.
How reporter privacy works
The ordinary content-report process and the copyright notice-and-counter-notice process have different disclosure rules. The Complaints and Content Removal Policy explains ordinary reporting. The DMCA / Copyright Policy explains what notices contain and what is passed to the other party, including forwarding a valid counter-notification to the original notifier.
What the reported creator does receive
When content is affected, the creator receives the reason for the decision and their appeal rights. Explaining a content-policy decision does not require identifying the ordinary reporter. Copyright cases instead follow the DMCA disclosure process described above.
Why this policy exists
Keeping ordinary reporters' identities private helps people raise concerns without fear of retaliation. That privacy statement does not replace the separate copyright procedure or promise anonymity for documents that procedure requires sharing.