Notes from someone else showing up in my icloud notes app

I opened my notes folder and under "All iCloud" I was surprised to see 5 different note threads created one week ago. I did not create these notes and I was actually at a work function around coworkers when these were created, but my phone was in my possession the entire time. All 5 notes were created within a 45 minute period and one note was very personal in nature. I have changed my password, but very concerned that someone else's info ended up on my phone and potentially they have access to information on my phone. Has anyone else experienced this and/or do you know how this might have happened?