What the GP describes is absolutely correct. It may not be all that common but it is a known pattern. That you haven't heard of it doesn't mean it doesn't exist.

> An alternative approach is to hash the passwords as usual and then encrypt the hashes with a symmetrical encryption key before storing them in the database, with the key acting as the pepper.

https://cheatsheetseries.owasp.org/cheatsheets/Password_Stor...