It's just a config for emacs. Sure it has some functions and life-cycle hooks for you to change a few things here and there, but in the end it's a glorified config. You delete .emacs.d and you're back to default emacs.
In emacs, thanks to Elisp, you can't really distinguish between a config and a plugin, because most 'configs' use actual code to (often extensively) alter the editors behaviour.
