To further prove it's a hoax, the Argentinean newspaper that broke the story has
a different version of the video up on its site in this version, our intrepid youths shine a torch at the malevolent midget before scarpering, they don't in the Sun's version.
So basically, either it's real and they were spooked by the same gnome twice, or it's faked, they filmed a few versions and rather stupidly sent different ones out to different media sources. I know which of these two possibilities I'm inclined to believe.
Besides, you can't really make much of the gnome out he's too pixie-lated.