Too much sharing going on behind the scenes. You can be pretty sure Google is able to connect all the dots on their system, imho.
Google Calendar users should be careful with how they name their events, or they might just end up sharing them with others. In an attempt to intelligently interpret event names, it appears that Google Calendar will also automatically invite anyone whose email address is mentioned in the title — at times doing so without notifying whoever made the entry.Google Calendar Bug Privacy Issue [theverge.com]
Google tells us that it's aware of the issue with Calendar and is actively working to fix it.