...meters per pixel...
Did they mean “pixels per meter” ?
Nope. At these distances, it probably is meters per pixel. Recall that Ceres is about 950 kilometers, or 950,000 Meters in diameter. . . and consider the field of view of the camera. Any thing that gets a portion of the surface would be 1/2 of pi X 950 or 2,984.5/2 or Columbus (grin). . . 1492 kilometers, 1,492,000 meters in the field of view.
The camera on Dawn was made about nine to ten years ago. . . and it's pixel count is not up to the level of modern digital cameras. So "meters per pixel" is correct at this time.
Oh, and the visible hemisphere would have approximately
567,450,173,000 square meters. Again, yes, meters per pixel.
When you get to fractional pixels per meter, it’s more convenient to use meters per pixel :)