Without googling a bunch, I don't know if the 'dog' in the story is called a mastiff, or just described as one. Seems like it would have to be something like a mastiff, because frankly smaller dogs have trouble killing an adult human one on one. As mean as an adult pitbull can be, a single dog usually can't kill an adult human... sure, they can tear you up like a chainsaw, but it usually several pitt bulls when it's a healthy adult that gets killed.
But I'll tell you what, the difference with an animal like a mastiff if it was truly trying to kill you would be terrifying. I was playing with the dog in the picture when he was about 160 pounds... still a wee pup. And while I tried to hide a toy against my chest, with my head tipped forward... Ian was behind me trying to get to the toy, and out of frustration, grabbed me by the head!
Yep, lower canines on one side of my head, upper canines on the other side. I'd never had my head fit inside a dogs mouth before. So I gave him the toy. Smaller dogs grab you by the forearm, or the calf/ankle... and mastiff breeds can grab you by any part of your body they want. (this would include St. Bernard and GreatDanes) And I can also tell you when a 200+ pound dogs hits you below the waist, you're going down as if clipped by a linebacker. They have 4 feet planted and you don't... you're going to loose. Luckily most mastiff breeders have been VERY conscious of breeding real aggression out of the breed. Finding a really mean one is basically impossible.
Bullmastiffs are a different story agression wise. Some Bullmastiff bloodlines are still a bit agressive, especially towards other dogs. They were originally bred to kill a poachers dogs after all. (and be able to take down the poacher as well.) Almost any hunting dog could keep away from a pure mastiff... they aren't quick by any means. Bullmastiffs were bred back down sizewise to get some functional skills that the oversized giant breed had lost.