The cultural and historical context is important. In Joseon era there was almost 0 % chance of meeting anyone from Africa or Europe. The king could maybe invite some foreign envoys to the court for trade purposes, but in old times they mostly hosted events for Chinese envoys.

Even today some people in Korean villages have never met a foreigner. I live in small country in the central Europe and trust me - I have seen black people only on TV, and met one in my late 20's in bigger city where I went to study university. Central Europe was always very "white" place and it's not insult to anyone, the same as in Joseon era there were probably almost no black people as well.

So it's totally normal for someone to have cultural shock to meet a foreigner for the first time. Trust me, it's not an insult. It's just human experience of meeting new people who come from different places and cultures. Now the world is more global, we have more opportunities to travel, so the chances are much higher to meet foreigners and even become friends. :)