Considering that the direct had ALL pokeball mons, but there wasn't any trace of Chandelure, Koffing, Gastly, Zekrom, Reshiram or Milotic, it has chance mostly as a not pokeball mon. or just was added after the fact.
Yeah, I'm guessing it's one of those two. Then again, we can't expect too many Gen VI pokemon to begin with, considering Greninja's inclusion was chosen before X/Y were far in development (or something like that?)