Well hopefully he means its open and not enclosed like the Oblivion cities I would like to see a return to open cities I hope a bunch of monsters just dont rampage threw the town, Morrowind had no problem with that so I dont see why Skyrim would...
Like every BGS made game, exteriors are consisted of big cells linked together, there are literally hundreds of them in Fallout 3 and Oblivion that make up the big open wilderness.
In Morrowind, the AI packages of NPCs and creatures did not allow them to travel through these cells, while they could chase you, eventually they would reach the point where they would stop and come back, those limits included cities, once getting near a village / town the NPC / creature would stop chasing you and return to it's original location. Because of that, there were never a single issue with creatures attacking NPCs inside cities.
In Oblivion, this changed, NPCs and creatures could travel through multiple exterior cells and follow you whatever you went.
In Fallout 3, a lot of settlements were wide open, this allowed NPCs and creatures to travel through, occasionally a mad Deathclaw would venture into Girdershade and kill Sierra and Ronald if they were outside of their houses, or attack one of the brahmins located outside.