"And at the end of days, justice shall fall upon the world of men"
I find it extremely unlikely that there is any other falling significant object in Diablo 3 other than the star, and as such I believe that the narrator is making reference to the star. This can also be seen when during the opening cinematic revealed at the VGAs when Deckard Cain, seeing the effect the meteor was having upon entering Sanctuary said:
"And at the end of days, the first sign shall appear in the heavens. Justice shall fall upon the world of men."
Later in that same video, he says:
"It has begun"
This suggests that Tyrael, the Archangel of Justice, is the star that is seen.