Given how often these poor fish are left to die after having their fins eaten off by sea lions, and how often they rub against anything they can find to remove parasites, it's hard to see how the fish was any worse for wear from what is clearly redneck behavior. If they were protected and/or the riding could somehow have injured the fish, I'd see the outrage.
As it looks to me, the fish didn't seem to mind and the redneck wasn't trying to hurt it. Not my cup of tea, but not particularly horrible either. I have no idea how "frightened" it must have been, and I'm not sure anyone has a good handle on what kind of emotions/fear responses these fish are capable of having. It certainly didn't look panicked, but I'd be happy to hear evidence that it probably was experiencing some kind of severe response to being straddled and somewhat restrained.
Still, if they're legal to catch, I don't see much of a problem with a brief ride not intended to inflict pain/injury even if it would have provoked a fear response akin to being hooked. Sounds similar to catch and release to me...just less hook and more redneck. It's the redneck behavior where there's intentional infliction of pain that tends to rub me the wrong way.