Atmospheric conditions needed that blocks all bright light during sunsets and allows you to stare directly at the sun
I am familiar with this phenomenon. In London, in winter 1947, I remember being able to see sunspots with the naked eye. The sun was very orange, like the one in your photo. The reason I was able to see sunspots was,of course, that the London sky was polluted with fumes and the winter sun was low on the horizon, so the rays had a greater thickness of atmosphere to penetrate. Much of the short wavelengths were filtered out, while the longer, redder wavelengths were able to get through. Much the same thing seems to have happened when you took this photograph of Seoul. It is common knowledge that red wavelengths penetrate foggy or hazy atmospheric conditions better than shorter wavelengths.