Here's the question in question (sorry).
Is this some sort of default that happens approximately a week after a mod locks a question but doesn't take any further action?
Yes, some of the locks we set are temporary and will automatically expire after a set period of time. This time of expiry is hidden from users, though.
Not every lock is temporary; we can choose to lock a post permanently (until it's manually unlocked) as well. Again, whether a post is locked temporarily or for good is not disclosed to users.