There's not much Tirian can think to say in response to that, and not much he really feels inclined to say--as much as he respects and admires Lucy, he's not in any mood to subject himself to further scrutiny.

And perhaps Lucy would press further, if he seemed less resistant to it, and perhaps if she did, their ride would become less pleasant.

But it's a pretty fall day, and perhaps neither of them wants the afternoon to become less pleasant, and so they simply ride for a while, companionable, if silent.