Like Coon said, Google is being weird lately.
This isn't really weird, it's just the "Google Dance". When Google starts recalculating page rankings, the rank for any page can jump all over the place. After a few days it usually settles back down.
One thing you will notice once Google knows about your site is that they come and visit a few pages almost every day. This could cause any particular page to show up on the rankings for a while, but the rank will likely change again when Google does a mass recompute.
I really think that Google was being "weird" at that time. They were doing a special kind of crawling and did things that were very unusual. If it was a normal Google Dance I would have not called it weird, but at the time the thread starter asked about his issue, Google was doing things a bit differently, therefore I called it weird.
Regarding your second comment, let me just add something. Google doesn't visit all sites, or certain pages of all sites. They only do that with some websites such as News webpages that update on a daily basis. Google does not go to sites every day that stay same most of the time. It's only the sites that get updated a lot that get new crawlings daily or weekly.
