It responds well to being resized (e.g. to fit on a mobile phone screen instead of a large monitor). Although, I think it is normally used to mean considerably more than the simple scaling being done here (e.g. I've seen designs where the text goes from two columns to one if the display is narrow).
http://en.wikipedia.org/wiki/Responsive_web_design
Right. His first example puts a scale factor on a 2400x700px image to make it "not too big" for smaller screens. That's responsive design the same way that the NES emulator on my old WinCE phone in 2003 (which had a touch display that only supported a single input touch at a time) was NES on WinCE.
