Having done many years of Staffordshire terrier rescue, rehabilitation, and training, I experienced it, and it's stressful. (Just a note that the dogs we rescued never started a fight or attacked other dogs.)
As for A, I feel for him, and of course, Finn.
Everything, though, depends on whether Finn is okay. It sounds as though he is not badly injured, but if A is not sure of that fact, then he should seek a vet.
What concerns me, is that sometimes a dog who is attacked suffers from stress, or even becomes afraid of other dogs, or ones who are the size, type, or color of the dog which attacked them.
That can translate into running away behavior, or fear behavior which comes out as attacking dogs first.
Maybe nothing will happen, but it can.
Is the dog which attacked Finn from the area, such as belonging to the business or a neighbor, or was it just there randomly?
I would call AC - or whoever took them over there - for 3 reasons.
1 - The dog should be held to make sure that it's not diseased.
2 - They need to assess whether or not the dog possess an ongoing threat to dogs, or even people (2 year old?).
3 - They need to deal with the dog's owner.
The url for this board is in the url bar at the top of this page. It is:
I hope that Finn is not badly injured.
Love All Life, Thank You For Posting! :)