if it was this region my guess is they would need to use one of the other zygarde cores to trigger something, causing the two from kalos to come running and bring greninja with them.
You know if Ash catches Meltan, then I hope he does it for himself, not for someone else.
Cause I have this feeling Oak will ask Ash to send it to him for study, or catch it for the purpose of study.
I don't want that.
Granted I know Oak would probably study it if Ash leaves it with him later in the year, but as long as Ash is catching it right now for himself, and it works into his current team, then it's fine.