Ok, let's clear this out.
Aonuma said it's gameplay, not seamless gameplay, let's see how it's done.
When they make a teaser/trailer for gameplay they set certain cameras in debug, those cameras are not the one you'll be having when you play the game, they are specially placed, directed if you like, to catch certain footage.
Our scene starts with Link on Epona in a field. There are farmers picking up things in the left, some animals feeding in the right and other cool things. This scene is real time, in-engine showing you how the game looks and how NPCs, humans and animals behave, but the camera is obviously further back to give you a wide vista for the purposes of the trailer.
The action starts when a monster appears from the left and starts spreading chaos in our peaceful scene. Did the developers waited for that to happen? No, you are the one who, as a player, might or might not encounter it. The developers made it happen.
They wouldn't wait for the engine to spawn a monster for the trailer, they wrote a scripted event for it to appear.
Next thing we know Link flees and the monster gives chase.
Change of camera. How did that happen? No, the game won't have Resident Evil 1 set cameras. This cut was the result of editing, where they put together the footage caught in the previous camera and this second one, again for the purposes of a trailer and again that's not the camera you will have while playing.
Lastly Link reaches the bridge and the creature destroys it, another scripted event that may be in game, destructible objects is nothing new. Then we move to more traditional gameplay, two shots from the bow, you can even notice the animation interpolation there while Epona slightly repositions. The camera is again a little further back than normal.
To end the trailer another camera shows a slo-mo animation as link fires an arrow. This last action is scripted, put in slo-mo and shot with a moving camera to dramatize the situation.
Everything is still in real time, everything is still running on WiiU hardware, but it's shot in various angles and edited to give it a more cinematic and trailer like look. What we saw is no indication of cutscenes or QTEs, just a little bit of editing magic.
Hope that helped.