God as a concept is generally defined as the Supreme Being. Which translates to the greatest being in the universe...whatever that is.
If an alien species just happens to be the Supreme Being then obviously they would qualify as God. Though we prefer to believe that any being, which is Supreme would be greater then simply a supper human, even though ironically that is the only way we can understand such a concept.
Another problem with the Supreme Being concept is that even if we came in contact with such a being, we would immediately imagine a being, which is greater then it, hence debunking it from its title. Hmm...thats the first time ive ever though of that. Thanks onionmon
