It was in a calendar (this case G+). It's not going to know you don't want a reminder for something because it's not a human and it can't read your mind.

I'd rather have it remind me of things that I don't want to be reminded of than not be reminded of things I do.

The premise of google now is that it can read your mind. It's not my (the consumer) job to be concerned about implementation.

No, it's really not. The premise of G+ is that it predicts what you want to see. There's a massive difference between predicting and knowing.

It was a Google+ event with about 100 people invited. It felt like it was a cached notification that didn't realize I had already arrived.