Some more possibilities:
6. We are the extraterrestrial life that travelled with a comet or meteor on earth and developed to all existing life.
7. They visit us as gods and teach us, like some views of Egyptians gods.
8. The Aliens live undiscovered on earth.
9. Alien life that uses earth for vacation or hunting.
10. Other plasma-, energy-, antimatter life forms that can't communicate with us.
11. Intelligent life that is not interest in us.
The Sci-Fi geeks may know more.
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