It's just a projection, you're looking at the sphere of the sky as seen from a (stabilized) Earth position. When you zoom out, you increase your field of view beyond that of the human eye to encompass the whole sphere. Because there's no way to compress a sphere into a plane, you have to choose a projection; this is a common projection (stereographic) which lets you zoom out as far as 180 degrees, by presenting the field of view as if it were the surface of a sphere as seen from an infinite distance.
A fun fact I learned while visiting the Globe Museum in Vienna, is that they used to make globes in pairs; one would be a globe of the Earth, and the other would be a Celestial Globe which is a projection of the sky onto a sphere. What you're seeing is a celestial globe
