Where did recent contacts come from?

[iMore Question]

I went to send a message to my son and when I typed in the first letter of his name (because he has more than one number) a list of people popped up, some I don't remember texting. When I clicked on one, it took me to a person and asked me if I wanted to remove from recents. I don't even recall texting that person at all. If I sent a text a year ago, would my phone "remember" said contact and keep it?