That remains, in some ways, one of the funniest videos on the internet[0], but the dog owner was and is an absolute moron. Imagine letting your dog off the lead near a herd of deer. That incident took place in a literal deer park. They're not livestock, per se, but, no surprise, the outcome is about the same as letting your dog off the lead in a field of sheep, and the consequences could have been much more serious.

[0] To the point where we briefly considered naming a dog Fenton, but then realised the humour would wear off pretty quickly and it wouldn't really be fair on the dog.