Google uses crawling bots, little programs that scan the internet from link to link, taking note of everything they see, and giving everything a level of importance.
When a webmaster makes a website, they usually also make a XML site map, this site map is uploaded to the websites server, and then you send a report to google, telling it where it can find the site map. Google will send over it’s crawlers and take a look at your site and list it. Each time a crawler visits your website, google updates the websites listings, and new results show up.
When you tell google about your sitemap, you can also tell them how frequently your site is updates, and google will send its crawler bots to your site that often. So, fluther more than likely has told google to check for constant updates.
It is not quite enough to tell google to check for constant updates, when google visits they need to see updates, if they dont see any, they wont crawl your site so often. So basically, fluther shows up more or less instantly, because google has picked up that it is a very relevant site to whatever keywords you used, and that it is updating on a regular basis.