I disagree with that statement. SETI folks have stated time and again that their equipment is not designed for and admitedly CANNOT detect leaked EM radiation, i.e. TV or BMEWS signals. For example, Ariciebo can't detect such signals from over 1LY away. So that is a false straw man premise.

SETI has always been about detecting powerful transmissions designed for contact. Our radio receivers would need to be many Km in diameter to do otherwise.

It took a long time to overcome the radio chauvanism but finally the SETI guys realized that laser transmissions are a far better (easier) way to beacon contact info across the galaxy. (Yes, I know that folks like the innumerate SM cannot comprehend this) Much better SNR and really easy to detect on the receiving end. Transmitting, a superpowerful laser can spray blips to thousands of candidate stars over a couple hours. An optical telescope is inherently a wideband detector able to detect 'billions and billions' of different optical wavelengths. In contrast the SETI folks started with one or two 'water hole' magic radio frequencies and then built racks and racks of eqpt to signal process their way to broadband detect a billion radio frequencies.