I don't know what case you are referring to. The only ones I'm aware of concerned whether the feds could send guardsmen overseas for their 2 week annual tour. (To places the (usually 'Rat) Governor didn't want any US military sent. The Court ruled that during the annual tour the Guardsmen are wearing their federal hat, and the governor has no say in where or how that annual training is conducted.
But, as long as the Guard is not federalized, over which the governors have no say, they are under the command of the governor who is free to send them anywhere (within the state or outside with the permission of or at the request of the governor of the other state) she/he chooses.)
BRAC wanted to shut down one of the PA air national guard units and close a base, and the court ruled that they couldn't do that without the approval of the governor.