Jeff is correct, I don’t write release notes for stable releases. The email you received is a standard email, shared by all Discourse instances. It doesn’t know what branch you’re on.
Stable point releases only include critical bug fixes and security patches. Unlike our normal releases, which contain hundreds of changes, stable point releases generally have less than 10, many times far less.
You can see all the changes at https://github.com/discourse/discourse/commits/stable. Look for “Version bump to v{current version}” and “Version bump to v{previous version}”. Anything between that is the changes. In the case of v2.5.2 there are 7 changes. 3 security, 2 follow ups to the security changes, and 2 critical performance fixes.