How did they animate the character opening the door on YouTube website?
Here is the link to the video that showed it.
I believe it was a transform behavior. If you arm that and record scale X or Y in two positions (closed and open), then blend between the two takes, you could get a similar effect. There may have been some rotation in there as well.
When the next version launches, you'll be able to dig deeper into the file - everything for the tutorial was done in Character Animator and there's a lot of cool stuff to check out!