Serebii's opinion is the same as anyones else, like you and I, they have just about as much information as anyone else at this point in time.
Also what's your beef with the OT? what does it matter? regardless of the OT we now have Diancie. So sit back, get on your knees and bow down to the most beautiful pokemon according to the reveals from Nintendo and the ingame triggered mini event (makes Milotic yesterday's garbage).
Anyways, we all too can wait for the "official" Diancie too, but for now get to enjoy this Level 15 Diancie, regardless if it's a modified Level 10 Torchic Wonder Card.