Exploit/Bug? Moving beyond the walls of an arena/starting shield

I've just gotten out of a Garuda HM trial in which two players teleported outside of the starting shield (or whatever you like to call it), later followed by teleporting outside the edge of her arena (beyond all that wind) where they could be targeted but were considered out of line of sight. When asked if it was some kind of exploit or hack one of them simply said "Magic Broom". I've taken screen shots for verification, but I've never had to figure out how to go about it. Perhaps other players on this forum have seen these two at work, players by the names of Isnow Blacklisted, and Strumer John (Lalafell Black Mage and White Mage respectively).