I think its because of the distortion in the picture. Organic shapes like rocks/terrain looks okay with distortions but the rover is more sharp and inorganic. The way it looks is kinda odd i dunno
It's kind of interesting how everything has a square sense and orange color in that world, some other pictures look what it looks like coal too in the nasa gallery
The rover's Mast Camera, or Mastcam, provided the panorama. Malin Space Science Systems in San Diego built and operates Mastcam. A division of Caltech, NASA's Jet Propulsion Laboratory in Southern California built the Curiosity rover and manages the Curiosity rover for the agency's Science Mission Directorate in Washington.