The Twilight stars, who are rumoured to have been dating since they met on the set of the vampire films, headed to the small island's Ventnor resort for a break.
They were snapped by a youngster who was shocked to see the movie stars - and Stewart is in disbelief that they were caught out.
She tells Britain's Sunday Telegraph, ""That was some kid, not paparazzi, who took that shot. That's the kind of thing that just baffles you. I can't believe that came out.""