What? If it is an alt for an R&F civ then it has to require R&F. GS has nothing to do with it.
I think the argument is that you wouldn't need either expansion to play the new leader with the new civ. It doesn't completely rule out this possibility, but the wording on the Civ website makes it sound like it's going to be an alt for one of the R&F civs only; every other possibility would technically be playable with just Vanilla or with Vanilla & GS.