First, I wouldn't call him a tsundere, he just has a hard time portraying his emotions so he seems cold. Second, my theory is that he really did ignore her at some point, but then realized along the way it's not the best thing to do as well as the fact that he lost her at some point. Maybe he thought he couldn't catch up on all the years they've lost because of her growing hostility, hence the lack of communication. Maybe there's another reason. But now that, for once, his daughter shows some interest in what he believes is father daughter bonding time, he tries to somehow render his feelings and thoughts.