That's not a completely accurate statement. FF Versus XIII is part of the Fabula Nova Crystalis like the other FFXIIIs are, but the only thing it has in common with XIII is that it draws from the same mythology. Otherwise, it is a completely separate world/universe. There are no ties to either of them. And from the gameplay videos they showed it looked a little more traditional. It looks like it was closer to being turned based than FFXIII is. It was also supposed to have an overworld map like FFI-IX and airships the player could fly. The feel of it was more contemporary with it drawing on modern day Tokyo for visual inspiration on the city.

FFXIII and the sequels are still turn based. An action RPG is completely different from what FFXIII was, it was certainly closer in terms of pacing, but it was still a turn based RPG like all FF games have been.