Even if they are not related, you might be acquainted with someone who has your last name. This is particularly true if your last name is one of the 25 most common names here in North Dakota.
We are all distinctive in our own particular ways. Even a little physical characteristic like a freckle makes you unique unless you have an identical twin. Even though you share a twin with another person, you still have a unique feature. Your name might not be very special to you, you know at least one other person who shares your first name...