Rheinland was neither Joyce's expertise nor within his job description. It was certainly not part of his mission and it would be unprofessional to release what little of his government's intentions he knew without instructions from the government. If it was up to him, he'd try to avoid the subject, but it was professional to find out what Kusari wanted with Rheinland. There are no truly informal conversations between diplomats.
"Rhein-Rheinland? I suppose... it's an objectively positive circumstance that their civil war is over. Do you have anything specific in mind?"