If you look closely in the trailer, you'll notice that the fireteam is invading a Cabal base, which is supported by the Slug Rifle in the opening shot, the corpses of Legionaries in white armor, and several other details. These worlds are supposedly repositories for highly advanced technology and anomalous objects / entities, lending credibility to the fact that they could contain miscellaneous objects from an entirely different universe (Paraversal convergence is already cannon in Destiny universe). This might have been super obvious already, I just wanted to make note of it.