This idea is cute, but it’s a poor substitute for a real writing tutor/coach/teacher.
It repeatedly returns: “Your response seems incomplete, so we set your score to the length of the original sentence. If we're mistaken, please drop us a line with a screenshot of this screen”, without any indication of how to fix the solution to be acceptable. I suppose it’s fishing for some specific keywords?
It doesn’t seem to have any full natural language model or conceptual model of the idea of the paragraph, so it can’t point out awkward or confusing phrases.
The proposed “par” and “record” sentences are not especially clear or elegant prose, or even especially short for conveying the ideas in the paragraph, and the metric (fewest characters used) is in general a weak heuristic for clear writing. The prompts don’t offer any list of essential vs. superfluous information, or even an explanation of the paragraph’s context and audience, so a proofreader/rewriter has to guess precisely what the author needed to say, and what the appropriate tone/style is.
I ultimately don’t understand how this game teaches writing any better than just trying to rewrite random sentences found in a book. Or for that matter, just having an email conversation with a friend about some random topic.