Right, I read an unstated assumption in the article that the only task at hand is to write out what you already know. It seems to completely ignore the potential goal to create and the block of not yet knowing what needs creating. This may be useful pragmatism in the sense of, "if you depend on work, and cannot do the job, find another job (at least for now)". But it does not address the unmet need to perform the original job.
Whether in writing, other arts, or even science and engineering, I think it is quite possible to be strongly motivated to create yet to have an empty mental hole where the target idea will live. Capturing all the qualities of the hole is not the same thing as capturing what you want, the thing that is supposed to be there instead of that hole.
You can struggle to find more external context or infer things about the absent target, but you are stuck until some kind of creative insight or exhaustive exploration drags it to light. Capturing the process or the meta experience of having this hole is not your goal at all, and so no amount of dumping what you already know will fulfill your creative longing. Some creative processes may be supported by journals or other intermediate work products, but that does not mean that you can make progress just by producing more such stuff either. You really can be blocked by a failure to induce new insights.
To say that you should write out what is in your mind and declare that progress is to assume that your goal is just to reach some metric of output. That the specific topic either does not matter or is already clearly defined. But writing/creative blocks can be about a future or hypothetical that hasn't been located yet, not just some reluctance to document what has already been imagined.