Huh. Must be that 'curse of knowledge'. It sure seems simple in hindsight! I'll be careful about that word in the future, though. :)
The sections following the opening describe how user action can be modeled as a program (i.e. user-action is an act of programming). The section titled 'environment is also a live program' shifts to the next level - i.e. user action is not only an act of programming, but an act that manipulates another program: therefore, an act of meta-programming.
Does that help clarify the connection?