0Hz is definitionally the lower limit of information-carrying frequencies (presumably this is not actually capable of detecting anything between zero and 1Hz - not that there’s much of interest in being broadcast in the micro-, nano-, or pico-hertz range anyway), and 20GHz is well into the realm of “millimeter-wave” broadcast frequencies. That’s ten orders of magnitude, and you only have about 1 order of magnitude more before you start seeing complete atmospheric attenuation on the scale of meters. So their claim that this is a genuinely general-purpose receiver is pretty much true, surprising as that may be.