Haha sounds like a horrible film. I will take your advice and never watch it. I'm not sure what to make of the movies claim that the aliens are 70% related to humans without more context (but from your description it doesn't sound like you get any). I would guess that they were trying to imply that there was an intelligent species that evolved on Earth in the past? And is now returning? Not too sure.
Genetic similarity alone does not really tell you much about organisms (other than perhaps their phylogenetic relationship). But it is incorrect to say x animal shares 70% of our DNA so they are 70% human. That makes no sense. For example, bananas have 50% of human DNA. But are bananas 50% human? Obviously not. The problem with the comparison is that genetics isn't simply a blueprint that can be read the same way for every organism. A banana may share the same amino acid sequences for 50% of its DNA but all of the homologous sequences may be expressed in different ways or at different times during ontogeny. Essentially, the comparison does not account for development. It is also important to note that the comparison does not account for junk DNA (which does not code for anything). So in the case of junk DNA, bananas and humans could share the same sequences but those sequences don't code for anything - so understanding entire genome similarities becomes less meaningful. Finally, the comparison is intellectually bankrupt because you don't get any understanding of the genes that are different, how much they differ, and when they were selected for. But ... as I said ... the comparison is useful phylogenetically... sometimes. I've explored some of this in a post before about humans and great apes. And I've had my own alien movie rant before as well. I feel your pain.