It's a given that with Hiei's unexpected collapse being the start of all this, the fox is concerned about leaving him on his own for too long. While inside the temple they could periodically check on him by peering into the room even if he wanted space. Out in the garden, by himself, there was no real way to tell how he was doing. Especially considering the way he was still so stubbornly resistant to any form of communication device across the three realms.

Of course, the plants there aren't nearly as potent as they could be with the influence of Kurama's energy, but considering the fire demon's unpredictable state, he can't help but grow concerned with the passage of time. Ultimately, it's the look from Yukina that motivates him to give in and check on things, even if Hiei would rather he didn't. While he doesn't exactly conceal his approach, the fox doesn't do much to announce himself either, stopping just at the edge of the clearing for a bit before speaking up finally.

“You'll miss dinner if you're out here much longer.” Whether Hiei even had an appetite yet wasn't really the point, at least this way someone can confirm that he's fine, and the fox has relayed the message.