Another system for live interaction with music is Extempore [0], for which you can code in either Scheme or xt-lang. There are some very impressive videos of it in action [1]. Extempore is a re-designed version of Impromptu [2] which was somewhat more restrictive in terms of platforms and editor integration.
I don't understand ChucK or Extempore well enough at a lower level (yet) to provide a good comparison, but I'm just happy to see people introduced to any music hacking tools. :)
I appreciate the level of detail the author goes to in describing the creation process. Very informative. I did this myself once, but using a patch I made in Max/MSP for drawing and listening to line segments on a pitch vs time plane. For this particular use case, I generated the input score with a Python script rather than drawing them manually. I found that detuning the sustained tones made the biggest difference in matching the original sound, which the article author mentions. Here's a video of my patch: https://www.youtube.com/watch?v=xl4C4zsy9LY