How much proof would have to be provided that the Google+ invitation was sent deliberately by the user? Sworn testimony from a Google employee? There can of course exist bugs that send invites erroneously that nobody knows about. Revealing of the source code and analysis by experts? Unknown bugs can still exist, especially in systems as large as Google's.
Stepping back from this particular case, what about apps that scan your contact list and automatically send invites and/or messages?
These situations aside, it's far too easy to accidentally send an invitation. Hell, I don't doubt that many people reflexively agree to prompts on websites they think they're familiar with. Of course the argument can be made that people with restraining orders must be more careful, but it just doesn't seem sane to me that people can get jail time for clicking a button on a prompt that most people wouldn't think twice about.