I am neither the authority to define "encryption at rest", nor am i saying "encryption at rest" is good wording in this case.

But from my understanding, "encryption at rest" is not disk encryption.

If you have a database with disk encryption, once the disk crypto key is entered an attacker could try to "do hacker stuff" and exfiltrate the WAL files.

If you have "encryption at rest", the WAL files are written encrypted and are decrypted on read. An attacker may get your WAL files, but they are still encrypted.