The code is self-describing because it's written in a formal language with precisely defined semantics. By reading it, you should be able to understand what it does.

Here's an "obfuscated" version of the code in from the paper:

  a = {
      b: function() {
          return Math.floor(new Date().getTime()/1000);
      }
  };

This function takes the number of milliseconds since 1970, divides it by 1000 to get the number of seconds, and rounds that value down. There is need for an additional explanation of what the function is doing.

Granted, this is a toy example, and I'm certainly not against comments that describe what the next x lines of complex code are doing. But the paper is about using metadata to help a computer, not a person, to understand what's going on.