Ask HN: How did my phone figure out my SO's name and that we were having dinner

Last night I was having dinner with my girlfriend and my phone gave me a notification saying something like "Silenced your phone for Dinner with $HER_FIRST_NAME $HER_LAST_INITIAL" (with the variables replaced)

The notification came from an app I've had for a while that puts my phone on silent when I have a calendar event, but I never made a calendar event for having dinner with my girlfriend. I searched all my calendars on my phone and found that there was never an event titled "Dinner with $HER_FIRST_NAME $HER_LAST_INITIAL", nor were there any calendar events for that night at all.

I can see how an app could guess that I'm having dinner based on the time and my timezone. But how did it know the name of the person I was having dinner with?

Edit: For reference, my girlfriend is not using that app, and she's using an Android phone, while I'm using an iPhone. This is the app that gave me the notification:

https://itunes.apple.com/us/app/autosilent/id474777148?mt=8