Pod restarts - init containers

I’ve been reading the documentation and am stuck on this concept from here:

A Pod can restart, causing re-execution of Init Containers, for the following reasons:

A user updates the PodSpec causing the Init Container image to change. App Container image changes only restart the app Container.

Can someone help explain this? How would updating the PodSpec cause the Init Container image to change, unless explicitly changed?

I am planning to use init containers to register the service with an API and dynamically generate a configuration file based on the response. I want to make sure I understand how pod restart behavior affects init-containers.

I think that is just poorly formulated.
You could (read “should”) open an issue on GitHub for it.
That part of the documentation gives a list of reasons for restarts of the Init Container and one of them being, the user changing the Init Container image.
The point of this bullet point is to make clear that a change of the App Container doesn’t not cause a restart of the Init Container.