Revealing important information in the out of character "thanks for playing" bonus chapter? What is this, Umineko?
Nice to have confirmation on the level of thought the author put into the setting, though. To a certain extent, we could already tell that the language was decently in-depth, but with the comments about clothing, for example, I'm more confident now that Ryouta's belt being the same design as the villagers' belts is intentional.
Anyways, the thing about Mi Yamu Tuu being confused with Miyamoto kinda reminds of names like Sara, Anna, Naomi, &c., which independently developed as both English and Japanese names, leading to some translators having to clarify "this character is Japanese." Art imitates life.