I wrote the explanation above. Just good content on a topic that gets a ton of searches, but a lot of people don't write about it in clean, understandable ways. At the time, the Bootstrap doc didn't explain it in the same amount of detail. Now that google recognizes the content and the backlinks and social proof via HN, Twitter, etc, it's just on a snowball. It's at about 50k visitors a month, mostly from Stack Exchange and Google organic searches.

Once a blog gets a few top 3 ( and a few #1) hits in a google search, it just snowballs. I consistently get more and more visitors each day, more retweets, etc etc. Like after today, my average visitor count will jump up and then stabilize at a much higher average than yesterday, since once content like this that is instructional makes waves, people just link it and tweet it exponentially and it never dies off. Really crazy how useful content and targeted organic SEO can work.