True, but any sort of manifestation visible at cosmic distances must necessarily posit a science based on physics somewhat similar to ours. ETIs who can build Dyson Spheres can also build radio telescopes, even if they have since substituted something else for their communications. Other than direct contact, such as spacecraft, it is difficult to conceive of interstellar messaging being carried out by any means other than some form of machine-produced and machine-detectable electromagnetic radiation. Even a hypothetical civilization that communicates by seeding space with engineered message-bearing viruses must still find a way to lift them off the top of their atmosphere and send them on their way.

What makes us special is that we can make things that perform functions biological organisms cannot. A cetacean civilization based on advanced genetics and biochemistry might be able to have a superior materials science, and even biocomputers, but it is unlikely they would ever develop steam engines, sailboats and telephones.

To evaluate the likelihood of detecting ETIs we need to determine the likelihood of intelligence evolving a technology based on symbol and tool-making. Social insects have developed a highly sophisticated technology based on chemistry without developing either tools or sentience.