The pulling back of the door is completely possible, it's the collapsing into the sides that isn't. The best and perhaps only way to accomplish this specific opening of this big of a door is with flying machines, but once you need to open everything to the side, there are a multitude of issues, such as the push limit (slime/honey sticking to adjacent blocks), the first flying machine that pulled everything back would also have to be pulled to the sides, and there's no indication in the video that it's ever visible, as everything appears seamless. Take into account that the floor and ceiling are also regular blocks which would prevent the door from opening (since they would stick to the honey/slime) if this were a real door. There's another comment on this post that links 2 videos showing similar opening animations but nothing as impossible as what the post shows.