Not having seen Black Beauty, I can't say how close you came to creating a scene that would call the movie to mind. (Which may have affected your score, if many others have not seen it also.) I don't see a valid reason for the large numbers of 1s and 2s you received.
Color, saturation, and hue are all done well. The subdued lighting does make the picture seem a little bit "cold". Using depth of field to pull the pony out of the background was a good touch. However the focus starts to soften just past the ears, and by the shoulders it was pretty soft. Which is what I think got you all the focus comments, as the focus at the eyes is good, with the muzzle just starting to soften also.
Since this isn't your animal, and not your property, you were limited with what you could accomplish. Personally, I wanted to see more. Movies are about action, and movement. Which is hard to convey through a single frame exposure. Be that as it may, that is what would get my 10 vote. It's a fine picture of a pony standing still. And given the circumstances of the setting, you did a good job with what you had to work with.
Beautiful horse. The focus seems a bit off. It almost looks like you needed a bigger aperture number, or it was too dark and it was lightened in post processing. If it was a bit softer, it would have a nice "soft focus" feeling to it, but there is not quite enough in that direction.
Probably a good job you put the name of the horse from that film other wise others might have been confused, for me though it is fairly soft allover which possibly you were trying to achieve as I remember a Balck Beauty poster once that was kinda soft and dreamy, good shot and good luck.