Stories like this will always vilify the dog, but it's incredible to see a cat actively protect anyone like that, I've never seen that in a cat before!
As a dog person, this is very sad to see

Apparently it was domesticated (can't have been that well domesticated to go for a child like that, even if he did it in 'play') I can only think that it was starved enough for it's prey-drive to kick in, but even then it doesn't look like it was a breed that has those kinds of problems.
Hard to say really, but either way the owner was responsible for the dog and let it get out, so it's their fault, not the dog's, ultimately (I know not everyone see's it like that). So it's the owner who's face I'd be punching the living shit out of, not the dog at all (again I understand people don't see it this way)
As someone with 3 completely bonkers whippet x's, and years of experience with big golden's and various other breeds. I can say with some confidence that most/all issues with dogs (as pets) are the owners fault, be-it through bad training, ignorance or badly treating a dog. It's alway sad to see any dog/breed get bad press because of how they have been brought up, especially when that then leads to people ranting on about them, blaming the dog, demanding they be put down etc.
Glad the boy is okay, it looked like the dog went into 'wragging it' mode so that wound could have been
a lot worse, surprised he managed to get up and run like that at the end of the video, but that's adrenaline for you.