XI = 11 actually, but mostly agreed. They may both be sci-fi but not the same type of movie which I would find difficult to compare.
I think he meant the "09" to refer to the year it was released.
And I agree - I enjoyed both films but they are vastly different. Prometheus is definitely science fiction (I'd even consider it an attempt to do "hard" SF) while ST is more of a typical action-adventure that happens to be set in outer space.