She doesn't need to thank him for stating what should be obvious. Han Solo might be a scoundrel and, occasionally, a swindler, but he's loyal to those he has committed himself to.

They were coming up on a break anyway, weren't they? He looks down to give his blaster a completely unnecessary inspection.

"When have you been childish?" That may say more about his perception of Kitty than her actual levels of maturity. His perceptions probably shouldn't be trusted. This is more true, maybe, when it comes to his father. "Sometimes I feel as though I've never met him."