Okay, though this seems to be someone who tries to imitate Midjourney using Stable Diffusion, so it is still not quite clear how Midjourney does it. Though it seems plausible that they would "cheat" in this matter in order to get something more artsy looking. (But what if you don't want something artsy, or not artsy in their style?)

Thats the value proposition of MJ I guess. Its easier to get something good out of a simple prompt, but you end up with a recognizable MJ look