Well it seems clear that Roman was set to win, Vince changed plans in the last week, and the only person outside of the two of them who knew was Roman (and the ref, during the match).
From there it's hazy. Everyone agrees there was a spat between Vince and Brock, but no one's sure if that was a work or not. Shane acting like he was going to step to Brock makes it seem like it was a work.
They did get a boatload of money from the Saudis for their show, everyone who's part of the Vision 2030 plan the Prince is doing is getting piles of cash as PR to rehab the image of SA.
Did they ask Vince to push the title change to their show? Did Vince just volunteer to do it because of the money he got? Like the number of licks to the center of a Tootsie Pop, the world may never know. What we do know is that Roman got made to look like a chump in front of 70k people, and that's going to be hard to overcome.