Completely False. Arceus hasn't even been revealed over in Japan (at least officially) and won't be until (more than likely) the next Pokemon movie. No event has occurred yet and none ever will until it's unveiled by Nintendo themselves. Heck, there's technically no event for Darkrai or Shaymin; if I recall right, they were just given out, Darkrai with Dialga's and Palkia's signature move, and Shaymin with a special piece of code that allowed it to transform into it's Sky Form on Plat.