Happened to me too a little different though I already was in her place just taken off my pants and Knock Knock Knock at the door.  She was all nervous too then said this must be another guy I had been talking too and said I will call him and tell him I am out for a bit and will be back in a few hours. she dials and my phone rings then she has a real confused look on her face.  she said hold on calls again and I hear a phone outside ring LOL  this guy had to know she was there if I could hear his phone too.  freaked me out took me a while to get fully comfortable if you know what I mean.  come to find out what happened was I was suppose to see her later that night then got off work early so on my drive home I called to do my conformation asked her if she would still be available at X time then mentioned I had gotten off work early and wished I had set it for this time.  She said come on over now so I did.  I guess she had gotten me confused with this guy thinking I was trying to say I would come later but could come now if I needed to.  not really her fault I can see a mistake happening but she should have paid a bit closer attention to who was who.