Kurama didn't find offering to go to demon world all that odd, considering he'd already done it when Hiei first fell ill. Of course, he also isn't thinking about himself or them and where they stand now, his focus is only on helping the fire apparition recover in whatever way he can. Yes, he is concerned and feels he has every reason to be, all things considered. There's simply no sense in beating that dead horse at the moment.

“You seemed to be in quite the rush, before.” He doesn't ask if that's changed for some reason, aware that Hiei is suspicious and not wanting to push him on the subject.

“I thought, perhaps, you might jump at the chance for some time alone. That is what you wanted, isn't it?”

He's already sending the message before Hiei finishes speaking, optimistic that at the very least it will give Yukina something to be positive about, even if Hiei is correct in that it does little to appease his worry.