He'd have to be a genuinely good actor to keep a straight face like that then, because how do you even fake nonchalance about that.
My theory is that he actually doesn't remember his daughter, but he knows enough about The Gap that he immediately understood what this meant, and a wave of dread washed over him as he realized there's stuff going on in The Gap without his knowledge. As chairman of the school, and the school being one of the access points, what if he's part of some faction meant to guard and control The Gap, and Sejuro is a 3rd party undermining him for an unknown reason?