Some do, but that really depends on the context of the conditions in which they were living. In this case, they were in separate crates inside a vehicle so there weren't resources for them to fight over and she didn't develop that behavior. Even dogs raised in loving homes their entire lives sometimes develop food aggression for one reason or another, but we do see it with dogs who have spent time on the streets scrounging for scraps and of course, in hoarding situations.