There has been a heavy debate as to whether this is real or staged, but I’m now leaning towards real.  Here’s a few comments from YouTube:

Actually that audio is exactly right for the type of lavs/shot gun mics that I use in my wedding videos. Usually you have a lav on the priest and another on the groom - often there’s a 3rd mic up near the front to capture any readings. So the audio is pretty much exactly right.

I thought the timing was dead on too (I have no idea whether it’s real or not) but there’s a solid beat while everyone processes what just happened, if it’s fake these guys are all superb actors.

It’s not fake…he falls near her and she backs up. He is grabbing to stop his fall, and grabs her dress. As she backs away she falls off the back of the platform and her dress is pulled by him falling. The priest tryies to grab her and falls, too. It’s not hard to figure out