Wait, Ms. Nina was white?? Am I just being stupid and forgetting even though this was already established or something?
it wasn't ever really established i think, but nina (i believe) isn't the most common japanese name, coupled with being a natural blonde and having freckles, these all individually are rare in japan, and all in one person would be nothing short of a miracle, and on top of that, she's the english teacher, so it's more so implied and easier to pick up on as a japanese person because these traits are all so uncommon
this is basically just confirmation though, and i will admit i didn't know until this chapter either