Once upon a time, back in the Neanderthal period, TVs had a single input: the antenna.
If you wanted to connect other video devices, namely game consoles or VCRs, you had to do so thru the antenna input.
Therefore those devices would modulate their video to an RF channel. In North America it would be either ch 2, 3 or 4. (55.25, 61.25 and 67.25 Mhz respectively).
To switch between video sources, one would have RF switches and lots of coax cable.
Some poor installations could leak RF signals, which probably was what you were picking up.