tl;dr: The bright object above is the sun, not the earth. The bright "object" on the horizon is a "doubling" reflection of the sun in one of the camera's lenses. It doesn't exist in reality. This happens when photographing the sun on earth as well with certain lenses. The earth is black and totally invisible, except that it's a tiny partial eclipse covering up a tiny bit of the sun at the top (clearer in other photos), which is why it's a little "flat" at the top. The photo is not the precise moment of sunset. The caption is entirely wrong.
I believe I have solved it, I described it in another comment:
https://news.ycombinator.com/item?id=43452888
tl;dr: The bright object above is the sun, not the earth. The bright "object" on the horizon is a "doubling" reflection of the sun in one of the camera's lenses. It doesn't exist in reality. This happens when photographing the sun on earth as well with certain lenses. The earth is black and totally invisible, except that it's a tiny partial eclipse covering up a tiny bit of the sun at the top (clearer in other photos), which is why it's a little "flat" at the top. The photo is not the precise moment of sunset. The caption is entirely wrong.