Riboku really is planning a slaughter feast for Qin army. I'm guessing all the soldiers from earlier castles who didn't make a move are going to form up a giant army and block off Ousen army which will completely isolate current army. The hype is real for the upcoming blood bath.
That was basically a cover used by Hara to fool fans, a means to keep the real threat of Heki to his enemies a secret. In all honesty Riboku information network and intellect skills are so good he predicted it would be Heki not Kanki that would be tasked with taking the city, that scared the shit out of him and everyone present there. The only wise choice they had was to save everyone while they could. Heki is a GG that fools his enemies, allies and fans all the same.