Receiving a signal would be one of the more chilling things the Earth civilization can ever experience.

Good thing if these guys would be on approximately the same stage as we are, but chances are slim. An answer from someone who knows about radio for 1000 years in much more probable than from someone who knows it for 100 years, as we do.

Meeting the technologically more more advanced European expeditions did change the lives of the natives of the Americas, probably to the better, after a few centuries — if we ignore certain details.