Impossible to say based on a news story which is probably only 20% true. However, some breeds, once properly motivated, are controlled very heavily by instinct. Take sight hounds, for instance. Once that 'rabbit' is let loose in front of them, not much on Earth will distract them.
Pits can be this way, once enraged. If an animal (or person) came out of the woods suddenly and with a lot of intention, that could have set the pits off into a frenzy. Once in a frenzy, friend and foe become blurred.
Impossible to say. My guess is, they'll blame it on Trump.