[throweway]

I think E.T. refers to alien. If he means from outside of Earth generally ... well that is tautological. So I assume he means aliens.

[maaku]

Extra terrestrial is a astronomical term of art that means "not of Earth." E.g. not a satellite. His usage was correct, your interpretation was not.

[scrollaway]

How is it tautological? Signals like that can be terrestrial in nature. In fact, recent story:

http://www.wired.co.uk/news/archive/2015-05/05/microwave-par...

[throweway]

Yeah but i dont think he was saying no comet implies no microwave oven. Oh i dont know what the ancestor meant maybe we should ask him or her or it.