Would they bother to arrange all this just to entrap Xiao Yan? It seemed to me the ritual was real and their main preparation was the number of Dou Venerates they have. Being so arrogant, I'd imagine they didn't expect Xiao Yan to arrive, if indeed he planned to arrive, with forces that could ever match theirs. But who knows, if this really was a huge trap, it at least means they do take Xiao Yan extremely seriously. Far more seriously than the whole Pill Tower, for example.