Because there's more often other noises in demos.
I also was going to apologise for "speaking" in a way that was uncalled for, but your response made me not want to do that anymore.
I think you think that I meant the phone wasn't supposed to be there, like it wasn't supposed to ring in the middle of their recording, but it most certainly was. It'd be a pretty weird coincidence if it happened after THAT line, which is about a phone.
Your reply just made it seem like you misunderstood what I was trying to say about the phone being there.