Board Thread:Support Requests - Getting Started/@comment-1036245-20130623201635/@comment-1330470-20130623203413

By editing the CSS files of the wiki, wiki admins can color links to the userpages of any user they like. It's usually used to highlight admins, but theoretically you could pick any user and highlight their names.

Check out c:animalcrossing:Mediawiki:Wikia.css. Down at the bottom:

Some of this code seems to be broken, but that would appear to be what's causing the username highlights.