I wonder if this is another Bioshock Infinite scenario, where a sizable portion of their e3 demo was ingame and it was running, but it wasn't game ready code, it was made for very specific proof of concept contextual situations. Many teams treat their e3 demos like their midproject vertical slice, where they still take a lot of liberties and they'll figure out how to do it for real later.
Anyway. This I think can be dangerous and leads to unrealistic expectations from gamers and no less problematic for the devs. When they get back to the office stressing out how they'll actually turn what was shown into a full game.
This is all speculation of course, usually naughty dog does deliver in terms of quality always, and I'm a huge fan of everything they put out.