It could just be the picture, but is it grounded to the hanger and not the ground from the feed line? That looks like some form of conduit grounded set up and not a Romex line so that might be ok, but I prefer grounds to be to something that can actually act as a ground and not just a box like that. Also, are there three hot wires and only two neutrals?
I see someone is used to new construction (actually it is grounded to the rest of the house/a grounding rod)- it's two separate romex lines from the attic - one to the switch, one to the circuit (I think). One line is hot to the fan, neutral to the other line's hot. The other line is neutral to the fan, hot to the other line's neutral. Both lines have their grounds tied to each other and the fan
