It has the possibility to be hacked but it may not be hacked.
The Diancie event was released in Japan, North America, and Europe. Germany is in Europe. Until we get it's stats, moves, EVs, and IVs we will not know. It also doesn't matter if it's in a Cherish Ball, although it still may be hacked. If it is in any other ball than a Cherish Ball it's hacked.
If it does not have the Wishing Ribbon, ->
it is hacked. If it does have the Wishing Ribbon it is most likely not hacked. (I don't know if you can hack ribbons on to Pokemon, comment and tell me if you know)
Hope I helped!