Phone Etiquette

So the phone just rang and I answered it with a (professional) hello and received "yes." as a response. And nothing else. So I said hello again, this time with two question marks and got "yes." again. I finally asked "Can I help you?" and there was some confusion on both my part and the woman's part. Turns out she had been transferred but someone had misdialed the last number. I looked up the right number for her and she was on her way.

Who response with "yes."? AND NOTHING ELSE? Never once did she explain why she called me. I didn't call her, I don't know what's going on. At first, I actually thought it was a child who called. Who taught this woman how the phone works? Am I psychic and just don't know it? (I guess I'm not a very good psychic, then.)