Now that the English translations are out, I can definitely say that Juvia seemed to be under some kind of influence by Touka. Likely her memories were altered in some way, and she managed to break from it for a second to warn Gray.
I love that Gray was able to pick up on things rather quickly, as he know his girl well enough to see if something’s amiss. Right now, they’ll have the titanic wood dragon god Aldron to deal with, but I have no doubt that Gray will take heed of Juvia’s words. Things are getting intense!