I used to get notifications about coworkers meetings as well, but those were on meetings that I had scheduled for them in Google Calendar - even though I was not in the meeting, the fact I scheduled it somehow triggered it as notifying me once it got synced into the Apple Calendar.
I'm having another similar problem, without a fix. Even if I hide a coworker's Google calendar in the Calendar app, it still shows up when I ask Siri to retrieve my schedule. It only shows up in Siri's view of my calendar, but not the Calendar app. But if I click on one of the coworker's entries in the Siri display, it takes me to Calendar with the coworker schedule unhidden.