How did a random person's contact info end up in my contacts?

[AC Question]

I was going through my contact list and noticed an unfamiliar name with a local number assigned to it. Even weirder, I could not find any online record of the person's name online. I do not leave my phone unattended and I don't use any contact sharing apps (like Facebook, Whatsapp, Skype, etc.) on my phone. What are the possible explanations for this?