It was definitely arson. Disney hired a few guys to come over and douse some slide pieces in gasoline and set them ablaze. They were worried Volcano Bay was going to take much of their business, and knowing their expansion plans to BB and TL were going to take too long, they knew this was the only possible action to take!
(Okay, I jest...but it does suck this happened. I was actually going to Wet N Wild today until this happened...now a change of plans for the afternoon.)