Interesting. I'm familiar with the street/documentary thing. Yeah, a mall is "private property" but it is open to public and therefore to me acts similar to public property. Despite this, security in malls can still ask you to stop, however they, nor any other security cannot confiscate film, digital media, or camera equipment (at least not without a warrant, as far as I know).
Pretty sucky what happened to this kid, I'm glad I've never had to deal with that or see someone deal with that. It is funny how the security couldn't seem to comprehend the "I can't delete the photo...it's film" thing. The news article says that the mall said the teenager failed to comply, well he couldn't. Unless he opened his film door and ruined the entire roll (or at least a portion of it...depending if he left it open and exposed) he could not "delete" the photo.
I've dealt with this very issue numerous times in photographing daily life. What's strange is it always comes from people who are definitely old enough to remember film's golden age. People just can't comprehend it and then get all fussy because you aren't doing what they tell you (because you can't). Very frustrating. It shows either how little they're actually listening to you and what your saying or how poor they are comprehending the situation at hand.