I don't think there are any zoom hacks involved. Probably player positioning and 3rd camera angle.

when you stand closer to the edge you can almost see the entire arena.
The father you are from center the more you will see.

You can see it here when the DNC goes to the edge to kite.
If they had the camera slightly vertical in the video, I think it would look similar to the picture you posted.

At least i'm hoping this is the case ^^"