Inside of Universe Sandbox textures are references as numbers: 1, 2, 3, 4
For example (just making up these numbers, they depend on the order the textures are loaded):
That earth texture is number 23.
Jupiter is 21.
The Milky Way galaxy background is made from 2 square textures, numbers 10 and 11.
And the UI textures are made of 3 different textures: 1, 5, & 6.
Somehow the background texture got mixed up with the UI textures and is displayed on the spherical background object. That's what happened here.