I had something like this happen to me but I was doing one of those kill order beacons on patrol for the Cosmodrome. Usually it's something stupid you have to kill like a dreg or vandal that Cayde says has been plaguing the area. It took me back to where you start off the game in the Divide and back through the ventilation shaft. I get there thinking it's a vandal or that Servitor that's there but a freaking Archon priest with double swords pops out of that huge hole in the wall and starts comin' for me! I didn't catch his name because the fight was so fast and crazy. It was an epic fight and the best patrol beacon I have done so far. Was really glad I got to see a world boss out in the wild.