While allocated sMerits to merit sources is specifically for particular boards. That is why every merit source applicants have to indicate their interested board in the application as Merit source then Theymos have to review the necessity of granting the applicants request.
It's wrong statement, there is no such necessity for merit sources to spend merit on particular board or local board, users shown interest in helping their local board because they feel where there is lack of merits that shows how they intend to merit when they are accepted but if they doesn't want to or merit any post apart from what they mentioned in their application isn't wrong and free to do it as long as there is no abuse happens.
Putting the statement in different form so you can understand it.
Merit source are specified on particular board for awarding allocated sMerits services.
You can't apply for a merit source without specifying what board your interest is but as a regular forum user with sMerits received from other users on posts, you can still award sMerit randomly as desired.
And yea merit source that does not actively award sMerits from the designated board can be probed.