EmacsKeys is based on eventFilters installed on a QTextEdit or a QPlainTextEdit. It basically catches all keystrokes and modifies some internal state that make the resulting text in the editor look like it was using vim.

There are only a few files in here:

emacskeysplugin.{h,cpp} - interaction with the rest of Creator emacskeysactions.{h,cpp} - settings emacskeyshandler.{h,cpp} - the "real" event

There are some more hints for developers in emacskeyshandler.cpp