I too am a layman on this topic, but here goes: When you make a recording in most environments, because of power lines and equipment nearby there will be a mai

I too am a layman on this topic, but here goes: When you make a recording in most environments, because of power lines and equipment nearby there will be a mains hum in the recording at about 60Hz. This is true even if the recording device is battery-powered because it's in an environment with mains-powered devices. But the characteristics of this mains hum will change slightly over time depending on the load of the power grid (Edit: It appears this isn't correct; see ars' comment). So apparently what they're doing is recording the power usage over time in one place, and correlating it with changes in the hum in recordings. Since they're attached to the same power grid, the variations should be similar at the two locations. If the changes line up, then the recording was probably taken at that time. Similarly, if it lines up with time T=X for part of the recording, then to time T=X+10sec later in the recording, you know that about 10 seconds of audio were edited out. Again, this is my interpretation, and I welcome corrections.