Shouldn't it be something more like 20,000 km, since the equator is about 40,000 km long and we're looking at half of it? Anyway 6,371 can't be right though.
No, that's circumference - 3.14 * 12742 is approx. 40K.
You are looking at the Earth side-on, so you only see the 2D projection of the half-equator. (EDIT: I think it should be "1D projection")
Another nitpick - presumably our view axis is perpendicular to the solar system plane. The Earth would not look like in the picture, we would see one of the poles but slightly off-centered.
