Water is the only OB, correct? And the disc hit the side of the wall, rather than the top? Well, in that case, in my opinion, as the OB line (the edge of the water) is a infinite vertical line extending from the outer edge of those walls, your drive never went inbounds. It struck the side of the wall, preventing it from ever getting past the OB line. That would definitely make any stance on the putting area (even on the walls) illegal. I could certainly see a TD making (different) specific rules about that course and those walls, though.
DGCR #8162 | PDGA #45197 | PDGA Rating 958 | DGCR Rating 1002