I think the post you’re replying to saw was confused about the quote above. The person who’s claiming copyright by showing the claimed file started as their own image has to show that it started from their own image, and not just that the file could have derived from the image. Copyright cares about both the works and the provenance of works.
Stable Diffusion couldn’t be flagged under this pretense if a person used a prompt that was their own nor could they even be sued if they ran an image through it as long as there is no plausibility that it was made by a copyright work. The only thing I imagine a case working on is the actual training process of the algorithm rather than the algorithm itself for that exact reason.