Harry knew how tired Ron was. He had been tired before, himself, lulled by the empty woods he was watching and the endless thoughts going through his mind about the horcruxes. But he was also energized, because things were starting to happen. Possibly not in a good way, but the monotony was starting to break.
"I-- Luna-- I went to see her before," he said, distracted by her retching. Hopefully she was alright. Maybe it was good that she was throwing up some of the drug that they'd given her? "I only meant to see if I could send her a message by Patronus, but we ended up talking, and --she was different. Not as affected as everyone else, I mean. And I told her to send her Patronus if she needed my help."
He gestured in Luna's direction, not sure what else to finish with except, "She sent it, and it wasn't safe for her to stay there, so I brought her back. I don't think we were followed - I didn't see anyone around."
Was that a good enough explanation? Harry was pretty sure he'd covered everything. Well, everything except for what Luna had told him, but she'd said she had more to explain, so he could let her do that when she felt a bit better.