I just mean person Y (the alien) telling person X (Earth) that whatever person Y is person X is: if I were the alien, knowing that reality on Earth is more than likely to be replicated many times throughout the Universe, I'd be prepared to tell the inhabitants of the planet I was visiting that they're as much why reality exists as any other life form in the Universe.
Specifically, assuming the inhabitants were humanoids, I'd reflect things like movies and art, nations and news media, perceptions of nature, hobbies, the reality of migration, internet sites, simply anything I could think was the existence of Earth.