Looking through the vanilla files, there are no similar MESG entries for the stones. I'm guessing Enai has recently added them for some sort of Condition? It comes in during Andromeda v1.06 onwards - wasn't in v1.05. Appearing with just Skyrim.esm, skyrim.exe, update.esm, dawnguard.esm and andromeda's esp; It obviously isn't a fault in Lexy's guide or YOT.