OP's confusion probably comes from the fact that some applicants apply as a merit source for a certain board. Like what others said, MS aren't restricted but, imo, they should atleast spend most of their sMerits to their local board. It's the reason why they applied and probably the reason why they got approved.
It's also my understanding.
I applied in Meta for merit source position because I felt that we don't have enough MS in our local board, Croatian.
I even have topic there where local users can report their good quality posts for merits
https://bitcointalk.org/index.php?topic=4265795.0But, if you check reported or suggested posts you will realize that a lot posts are from English part of the forum, mostly scam warnings.
I don't have time to read all forum so in such way I can find and reward good quality posts with merits.
I also reward other good quality posts from non Croatian members.