How to show a message to a list of article publishers using Rules?
The loop isn't checking for the current user, so it is showing a message for all the users in the list, like you describe.

You need to check that the current user is in that list.

To do so you really need the http://drupal.org/project/rules_conditional module.
It allows you to have conditions in actions.

So your rule would be something like this:

Event: After saving new content
Condition: Content is of type: Article
Action: Load a user list with views (using Rules Bonus pack - user list of article publishers)
Action loop: Loop (above user list)
  Conditional:
    If: Data comparison (Parameter: Data to compare: [site:current-user:uid], Data value: [list-item:uid])
      Action: Show a message on the site


However, if you say that the list of users is any user that has created an article, and this message is being displayed after a user creates an article, then you can be sure the user who just created the article is in the list of users who have created an article :)
So just show the message when an article is created. No other checks for users.