pass error to admin_notices on “quick edit”/save_post action

The admin_notices hook fires only once per page load, and isn’t fired when a post is quick-edited.

You would have to do it browser-side with javascript – that is, listen for when someone edits and saves a post (which is done via AJAX) and use javascript to display a message.

A quick glance at the javascript file responsible for quick editing (wp-admin/js/inline-edit-post.dev.js), and unfortunately there doesn’t appear to be a way of knowing when the AJAX response has been received.