PP, thanks for posting. That really helps. A couple of thoughts:
1) Okay, I don't see where the dog is giving off messages that he is uncomfortable. He looks like he's enjoying the attention until the bite occurs. Can someone who knows more tell me what it was about the dog's behavior that shows he is uncomfortable? Is it the fact that he is licking his lips? Just curious cuz I don't see it.
2) With regard to the owner, the tv anchor was kneeling down beside the dog and petting it for a period of time but did not have her face right by the dog until she leaned down suddenly to kiss it (or it looks like she wanted to kiss it) and that's when the dog bit her. While it obviously did a lot of damage (and I'm not justifying it), it was a very sudden snap and it really did look like a defensive reaction to the woman moving in suddenly. Yeah, probably the owner should have not let her kneel down besides the dog to begin with but it would have been difficult to say something about that on live tv. But once she was kneeling besides the dog, there was no warning that she was going to move in suddenly to kiss the dog.
Overall, it looks like a very unfortunate but not surprising defensive reaction by the dog, given the strange and new circumstances, and it probably isn't breed specific (don't know anything about Argentine mastiffs so can't comment on them).
And it's also a good reminder that there are interactions in our daily lives, where it's difficult to speak up and to stop what's going on out of fear of embarrassment and despite that, we need to remember that it is our responsibility to do so. I have no clue whether it occurred to the owner that this was a dangerous situation. After all, he was distracted by responding to the tv anchor and was not watching the dog. But if he had been uneasy about it, it was his responsibility to stop her from getting so close to the dog. That said, I can see myself failing to do that in order to not disrupt live tv. And this outcome is a good reminder that we should act and not worry about the potential for embarrassment!