I think the prompt is not much other than "puppies" and "kittens". Major, middle and minor features of the image can be controlled individually in some AIs (they can be differentiated using a Fourier transform or Gauss convolutions and fed into different discriminators) so I think:

major features (scenery) are controlled by the prompt (grass or couch)
middle features (text) are a source image that the AI is punished for straying from
minor features (details) are controlled by the prompt (faces and fur)

Or it's just Stable Diffusion that starts with a text rather than random noise.