Sleep is not a hard barrier. Things can filter through from your surroundings. In addition to this, we can just outright hallucinate things that we think are happening around us. For example, when I WILD, I will sometimes hear my wife watching television in the living room. We do not have a television. Other times, I will hallucinate conversations like you described, where I am sleeptalking. Sometimes I really was talking to my wife, other times I was imagining the whole scenario. Shit gets weird.