How did another person's event show up om my device?

[AC Question]

I'm using the default calendar loaded on my galaxy s4. Today, 26 Sep., my phone sounded a notification for an event that appeared in my calendar for tomorrow, 27 Sep. at 2:00 p.m. I did not schedule this and it and has nothing to do with me. I live in Sonoma County, CA. The event is an appointment at a cardiac institute in Mumbai, India. What?? How?? Have I been hacked? How common is this?