The secret is that lots of Emacs commands actually call Elisp code, not the internals of the editor―you can invoke help on a command and then navigate to the code of the function.

(I have to confess that this sometimes comes useful in adding customization to those commands.)

Emacs blew my Goddamned mind one day when I was using M-. to examine the Lisp implementations of various Emacs commands. One day I dug a little too far and tried to examine the source to what turned out to be an Emacs primitive -- but that didn't slow down M-., which happily jumped straight into the Emacs C source to show me the implementation of the primitive. (I had compiled this Emacs on my own, and apparently it remembered where it was compiled.)

Thanks for the clarification. I have to learn those magics someday.