It very well could come from the video output of the recorder.
Too bad we’ll never know since this story was obviously just fluff, filler since there’s nothing they consider important happening anywhere.
I say probably analog cameras, cabled to a distribution unit which feeds out to the monitors and the recorders (which may or may not be digital). The various feeds are usually buffered, switched and amplified in a muxer circuit with multiple channels going through a single chip.
Crosstalk between adjacent video channels can and does occur which can create a ghost image of one channel on another. So someone walking across a room seen by one camera, especially if it is a high contrast image, can bleed into another camera's feed.
THAT is the horse that belongs to those hoof beats, I believe.