Thats from early footage of a Stalnox near where it ended up being in the actual game

This is just the trailer of the game so you can find much higher quality from that video instead of a camera recording a video of it being shown on a screen.

It looks like a Stalnox to me, but I'm not sure which one it's showing. 

I was at the Legend of Zelda Symphony of the Goddesses last night, and noticed this giant monster I hadn't seen before in the game. Do you know what it is?

seen here at 19 seconds:

https://www.youtube.com/watch?v=__x-wVNHj4Y&amp;t=19s


or here at 52 seconds:

https://www.youtube.com/watch?v=l5hEfjyGBss&amp;t=52s

Unknown Giant Monster in BotW