First of all, it's an approximate word count and I haven't actually tested to ensure that it's accurate, so maybe I didn't!
But, basically, I was 17 and it was summer and I just didn't do anything else for three days. There was no story planning or (especially) proofreading, so I pretty much just outputted a stream of consciousness into my keyboard. I also type ludicrously quickly.
As far as the site rating, I think it's highly biased due to being an admin. I don't think it's even remotely deserving of that ranking and I'm not just saying that to be modest. It's quite linear, has a super obnoxious maze, is entirely indelicate, is jam packed full of cliches, and the writing is bad and full of grammatical and spelling errors.