True, but our radio telescopes have also been improving. The Square Kilometre Array, under construction in Australia, would supposedly be able to detect "an airport radar system on a planet 50 light years away". I suspect that an advanced civilization 500 ly away would still likely leak enough radio for us to detect it with current or near-future technology.
Unless their technology developed along a completely different path, and the concept of radio waves is too foreign to them because they use an altogether different method of communication that we can't even begin to imagine.
