This just happened to me moments ago. The # wasn't saved in my contacts but it looked like a # I recognized. When the person answered, it sounded like one of my family members trying to disguise her voice to trick me.

I laughed and said, "you idiot, what do you want?" There was an awkward pause and then an "oh I'm sorry". I tried to apologize, stumbled a little out of embarrassment, but she hung up very quickly.

I sent the number a "Sorry, I thought you were someone i knew :(". Seems small, but I still feel very embarrassed.