It did find my "alt" (really an old account with a lost password), but the rest of the list – all users with very high match scores (0.8+) – is random.
Taking a look at comments from those users, I think the issue is that the algorithm focuses too much on the topic of discussion rather than style. If you are often in conversations about LLMs or Musk or self driving cars then you will inevitably end up using a lot of similar words as others in the same discussions. There's only so many unique words you can use when talking about a technical topic.
I see in your post that you try to mitigate this by reducing the number of words compared, but I don't think that is enough to do the job.
In case you haven't seen it, the author addressed this point of topic vs. style in a comment (albeit in a different context): https://news.ycombinator.com/item?id=43708474.
It did find an old account of mine that got banned, top of the list. I have to say 500 words for fingerprinting, that's mindblowing.
It focuses on topic a lot, that's true.