Is this an error in the translation?

https://preview.redd.it/o8mkkexcxzbh1.png?width=1920&format=png&auto=webp&s=3bbfcac6e0f09effcf5cc6af35d768f6e26b5d8d

Around the end of the page, Rudeus is facing the North Emperor Auber, when the latter mentions that he has already known Eris. Why is Rudy shocked, hasn't Eris mentioned that she trained under him and the Water god at the sword sanctum, when Rudy tells Eris that she might be facing both of them in their venture to Asura?