I'm not trying to be snarky or argumentative, but how would you witness someone "go over the edge on purpose"? What he did, was state he was going in the water, he went over the fence, through the brush and slid down into the water.
How would "going over the edge on purpose" look, if not like that? What other evidence would you need that it was purposeful?
Again, I'm not trying to be snarky, and his behavior is certainly bizarre. But unless he stood up at the edge of the moat, after having crossed the fence and run through the shrubs, and announced, "and now, I'm going to continue my mission to get in the water that I said I would do a moment ago by sliding down this embankment", how could it be more clear that it was purposeful?