The fact that Gray actually talked with Juvia about that matter shows how much serious this arc is going to be and we learned that he also has some secret power.
My opinion is that Ajeel may have got out of control and attacked FT on his own with his army, in the previous chapters he was quite upset that Zeref didn't wanted him to go solo against them, so that might be a clue.
I thought at the previous chapters that FT was being cocky but it seems they actually prepared everyone with Erza mentioning that CS is coming to help, they also probably alerted everybody in the continent, pretty much every guild has a connection with FT after all.