National Geographic's 2011 docudrama When Aliens Attack is as much a work of science fiction as it is a documentary. That means that, while much of the details incorporated into the film are grounded in actual science, and the film includes interviews with many real-life experts on the subject of astronomy, the production itself involves speculation regarding something that has never and may never actually occur. As such, the writers and director were free to shape the narrative in any way they envisioned. That this particular film depicts an invasion of Earth by beings from a distant world should in and of itself have suggested that the people putting the film together had liberty with the details and outcome.
It could logically be assumed that any life form capable of transiting many light years and launching an attack on another planet would be possessed of superior intellect and technology. After all, those countries leading the world in the area of space exploration are struggling to get back to the relatively close Moon, budgets and technological limitations having precluded greater advances in manned space travel. Unmanned probes have been successfully launched to the outer reaches of the solar system with one, Voyager 1, having actually departed the solar system for the universe beyond. Technologically speaking, that's not nothing. It is, however, a far cry from the manned mission to Mars that many space enthusiasts champion.
An alien civilization capable of traveling such distances as would be required would definitely have a technological edge, but that edge might be irrelevant in the Earth's atmosphere. Presumably protected within the confines of their vehicle(s), such life forms might not be capable of existing outside of those vehicles, just as human beings cannot exist on the Moon without being equipped with specially designed breathing apparatuses. In short, we just do not know what might be the actual physical characteristics of any such alien beings. Whether human beings would be capable of countering an alien attack is therefore dependent upon levels of knowledge and detail that we simply do not possess. Within the context of a speculative scenario involving an alien attack, then, any outcome posited could be credible.