When moving an attachment from one page to another and using the update links option, the correct behaviour is to update any page that has a link/reference to the attachment that has been moved.

What is happening in Confluence is that any page that has a reference to any attachment on the page will ALSO be marked as updated. This is incorrect behaviour as only pages that reference the attachment that was moved should be notified.
The resulting effect on production instances is that users will be incorrectly "spammed" with update notifications.

Updating Links updates all pages with reference to ANY attachment on the page from which was moved from.