Do we know whether those statements mean there was no sound coming from the TV (mute button used), or that they simply turned the volume down? I think someone could reasonably say muted when either lowering the volume or silencing it completely. I often ask my wife to mute the TV when I think I hear the kids upstairs and she always turns the volume down to a low level. The volume button is used much more often than the mute button and likely easier to think of on quick notice.
On my TV, the mute button goes to half-volume before it goes to full silence, which takes two clicks. However, the main volume control is a separate button that you have to hold down to lower it.
I guess whether W11 completely silenced her TV is something MoM can establish at trial, assuming there's any need to explore this point. It might need exploration, though, considering that Reich's "findings" have been publicized to potential jurors.
Is it possible that any extraneous voices Reich pulled out of this recording were picked up from background activity at the 911 dispatch end, or just some sort of bleed-through in phone transmission from another call? (Assuming, of course, he actually heard anything at all?)