Says here it is supposed to have a Classic Ribbon, so it's hacked.
http://www.pokecommunity.com/showthread.php?t=161576
#492 Shaymin
Pokemon Movie 08
Ball: Cherish
Level: 50
OT: ?????
ID: 07198
Nature: Random
Location: Pokemon Event
Event Moves: Seed Flare
Holding: Micle Berry
Ribbons: Classic
Dates: 7/6/08 & 7/19/08 - 9/30/08
I don't understand the hackers on GTS either (Or the legendary seekers, no im not giving you a Celebi for your Kadabra)
Someone traded a hacked shiny Tauros for my Chikorita yesterday. I don't get it