The point is, it's just a fake fact because it won't kill the dog, and it's also a dangerous advice because when you're reaching for the dog's front legs while he's in an attack mode, you're opening your vital areas (face, neck, head) for bites... If it's a life or death situation, use some kind of a weapon (stick, bat, knife, whatever), go for the dog's eyes, punch or kick behind the ribs, etc. If you're trying to protect someone who's being attacked, by far the best way to disable the dog is to get to him from behind, grab his collar, pull it up and twist. Once the dog is standing on his rear legs and his blood supply gets cut by his own weight as you continue to pull him up while twisting the collar, he'll stop attacking and will go limp in 10-15 seconds. If the dog is too large and heavy, elbow choke from behind instead. All of it is much more likely to work than the pulling front legs apart nonsense.