I’m hearing a few more things about this video that, whilst striking the horse was undoubtedly the wrong thing to do, it is a very short clip of what actually happened and failed to show the efforts that had been made to encourage the horse into the water beforehand
I am a follower of eventing, a horse-owner and my DD rides x-country but I am not sure that the efforts made to encourage the horse to cross the water prior to the incident, is of any significance.
I think most people who ride and are up-to-date with modern training methods know that it is totally counter-productive to keep on insisting that a horse goes in to a puddle or a lake, having tried walking through dismounted, ordinary encouragement once on board with hand and leg aids. Most people would take a break and work on something else for a bit, or approach from a different angle, or take more time and try on a different day. To get in to a stand-off with a 500 kg animal is pretty stupid (a) because a horse's strength is superior to ours and we should be relying on our brainpower to train them not brute force and (b) the horse will associate water jumps forever more with a negative experience. And that's before you introduce actual cruelty and hitting a horse with a tree branch which is morally wrong and reinforces the fear response.