Considering that is Cloud Gate in the picture ( as well as the two smaller buildings with the destroyed roof's), and the black hole in up in the sky, I believe they are referencing the Dragonlord and Gigantic Exceed fight, which they were probably still watching from afar after they fled the building.
As for the chapter itself... I had figured that it was the black hole that was being used to get rid of the super cell, so it's always nice to have a guess come true. Shame that it seems we didn't get much in the way of plot advancement, but I guess they did need to explain how he survived the super cell.
Perhaps next month then.