However, there’s one set of Mega and Primal transformed creatures whose status in Legends: Z-A remains unknown: the legendary Groudon, Kyogre, and Rayquaza. When Mega Evolution was first ...

which works very similarly to Mega Evolution (to a point where it might as well be the same thing). Primal Reversion is only for Kyogre and Groudon and is technically a different thing.