The deceased mother was talking to Gordon's guide who was then telling Gordon what she said. Or he was seeing/talking to her directly. It wasn't clear at that moment but I'm sure Gordon could answer that better.
Not all dead relatives hang around. The ones that come through a reading aren't just sitting around waiting for their shot, they are off doing what spirits do in the ether. But it's like receiving a phone call, "Mrs. Smith, your daughter is calling on line one. Would you like to speak with her?" to which Mrs. Smith may accept or decline.
However, some spirits do hover.
Read this blog entry for details on all this: Erin Pavlina’s Blog » Blog Archive » Crossing Over