I don't doubt that it was in-game is they say so.
However, since those atmospheric effects look pretty graphics intensive, I'd also like to know
- was it real time (i.e. did they render it at the framerate that was shown in the vid)?
- if yes, what kind of hardware did they run on?
Safe to assume a pretty decent computer. Unless we are at the stage of suggesting devs should intentionally make release footage on mid-range PC? At the end of the day, its still marketing and therefore they want to make it look as good as possible.