He's got a lot of karma (#2 according to her blog post). She makes a big deal of the date when she reached 10k. I think it's a safe assumption that's an important metric to her.
I didn't mean to imply that I know it, I thought it was clear that it was just a hypothesis on my part (assumption is probably a better word). I apologize.
It's fine that you think "that's probably it". Posting that as if you knew it for sure is unjustified and rude.