Sounds like the "light cone" idea - that information hasn't reached a place yet.

I suspect the objection is that with the age of the Universe and potentially life-supporting star systems there should be advanced civs from well before us whose "light cone" of evidence has reached us.

The objection to THAT being, given possible differences in perceptions of time or lifespans between us and 'them', it could be we are all "ships in the night" missing each other by wide margins. Overwhelming radio evidence may have bathed our planet for a century...while the Roman Empire pushed north toward the British Isles.

Another civ may transmit loud and clear very frequently - by that they mean, once every 400 of our years.

Or they are aquatic or live under haze and don't actually know about space or other stars. Or their own star.