It's hard to be sure.  To me, Paris Hilton always looks different depending on lighting, hairstyle, clothing, expression, etc.  She can look like a serious angular model or a breezy party girl.  In the picture in the AOL article, she actually seems more "genuine" and happy than usual.  But she does look thin (though the dress hides her stomach).  Is the camera lying if she seems more thin than usual?  I don't know.