Interesting concept up to now at least. As most likely many other readers, I'm really fond on how the author doesn't focus too much on the fantasy thing by using the context that "it's just everyday stuff" for anyone (except for the MC) and he's basically learning stuff on the go by watching or listening to others. The learning-stuff is well paced and doesn't feel too much theatrically injected.
For those who wonders, "theatrical injection" is how you call the common trope in manga where you got exposure of information such as a side character starting to explain things like a narrator after it happened in a way that would never actually happen in real life. As its name suggest, it's something you often see from live performance in theatre shows such as when a character move forward toward the public and shout loud what some characters are thinking or doing on the scene. In manga, especially isekai/fantasy stuff, you often get theatrical injection from the "intelligent" character in a party (usually a smart character with glasses).