I've always thought that the term "fine art" applied to commercial art that was suppose to be better than all the mundane banal crap art like Bob Ross or Thomas Kinkade. (I won't go into who I think photographic equivalents are).
Gallery art that has not become Art, yet. A label applied by gallery owners and salespeople, or modest curators. To sell people on the idea to part money from purse and wallet. When I see the term it usually is attached to some means of sales, a sign on a gallery wall or window for example.
I just assumed that fine art photography was that same sort of meaning applied to photography.