I would be extremely surprised if all the seven dogs attacked the walker. Far more likely it was one, maybe two/three.
I agree - and it is very possible overexcitement which has got out of hand, too. It seems that this poor lass fell, or was pushed over by the dogs. This is also dangerous - the instinct of most dogs, even when playing, is to grab and worry "prey" (for want of a better term) on the ground. Then when screaming and panicking starts the dogs get even more adrenaline-fuelled and things go from bad to worse and real aggression kicks in.
As you say - FOUR is an absolute maximum, and even that should depend on the breeds involved and their temperament, and how well those particular dogs get on with each other.
As you point out, young dogs, anxious dogs, tend to panic and distance themselves asap if there's even a hint of trouble.
I'd be interested to know the breeds involved, too, and how often they were walked together - if there was any conflict etc between them.