From the video:

1) they stack up all pickles/onions/etc in the front for ads.

2) the real burger goes in a box and the steam makes the bun shrink a little

Also, they didn't say it but they showed it:

The burger is cooked differently for the ad. I got the impression they were just grilling it to make it look good but with minimal cooking (I wonder if it's even safe to eat the ad one). If you've ever cooked a burger, you'll know they shrink when you cook them.