seems if you use the live preview as suggested above its not rendering the media queries. If you download the zip and open up the index.html file its working fine. Must be a error with their preview engine. Here's a screenshot locally on opera 12.12: http://i.imgur.com/RgIraby.png
Working fine for me in opera mobile (ios6) and opera desktop osx 10.7 and windows 7, its designed to be 1 column on mobile, expand to 2 column at 480px and then 3/4 column at 720px. So if your on mobile what your seeing is correct.
I'm using Windows 7 with the latest stable build on a 1600x1200 desktop display.
Here's what it looks like in Opera: http://i.imgur.com/yUcVqeN.jpg
In chrome it looks much different, it's aligned in the center with multi columns which I assume is the proper look.