You said yourself that their civilization had advanced to a highly technical level.

"They confirm what most reputable scientists have maintained for years: that a civilisation advanced enough for interstellar travel must be a peaceful one."

And civilization will advance a little bit more.

Egonian civilization had advanced to the point that Earth's sun no longer offered a sufficient power source for the Egonians' needs.

Agriculture and civilization advanced most rapidly in the valleys of the Andes.

The reasonable assumption was that any civilization advanced enough to receive the message would be able to understand binary arithmetic.

As civilization has advanced, the pack-bond (the tribe, the extended family) has been broken.

For instance, that every civilization technologically advanced beyond us must be peaceful, else they couldn't have lasted.

Hypothetical civilizations of this sort may have advanced drastically enough to render communication impossible.

They are intelligent, with their own languages and cultures, but their civilization has never advanced beyond a hunter-gatherer level.