This can actually be true, depending on how the system is configured.

For instance, if you and someone else use the same locally-hosted Stable Diffusion UI, both put the exact same prompt, and are using the same seed, # of steps, and dimensions, you'll get an identical result.

The only reason outputs are different between prompts is because of the noise from the seed, normally randomly set between generations, which can be easily set to the same value as someone else's generation, and will yield an identical result unless the prompt is changed.

It’s literally as true as it can possibly be. Given the same inputs (including the same seed), a diffusion model will produce exactly the same output every time. It’s deterministic in the most fundamental meaning of the word. That’s why when you share an image on CivitAI people like it when you share your input parameters, so they can duplicate the image. I have recreated the exact same images using models from there.

Humans are not deterministic (at least as far as we know). If I give two people exactly the same prompt, and exactly the same “training data” (show them the same references, I guess), they will never produce the same output. Even if I give the same person the same prompt, they won’t be able to reproduce the same image again.