What happened to me is almost what happened to your client, but a slight twist.
I unpublished all my articles, then did search for the word "module"
None of the articles were found, but I did have a menu item with the word module in it. It found the menu item and showed the link to the category, but gave me a page not found error when I visited the link.
It looks like if you search for a word that is also in a menu item title it will find the link title, and show the link. But of course there is nothing published there.
I left the articles unpublished. You can try it for yourself by going to
dashhelp.com and use the search box to search for the word module.
Sorry about that. I happened to pick a search word that was in the article and in the menu item. If I had picked anything else I wouldn't have got any search results.
Ed