The end of the "Project Moongazer" quest

The reply, specifically. What was that? Does this mean that the twins have received similar message hundred (or thousand) years ago but the response came just now? Or does this mean something else? And does the message depend on who the protagonist is? My protagonist is Aether, and I heard his voice in the message. Because if this message was indeed recorded before their arrival in Teyvat, it would make more sense if one of them spoke in both versions