I like how a decade of time has passed between posts. They also could have saved space by not storing the entire area of 320x200 and instead only a crop of it, since most of the screen is empty anyway.
Combination of both I would say. They clearly went for 2 bitplanes, which allows for 4 colours. Which is 16,000 bytes at 320x200, instead of 40,000 if they had used 5 bitplanes.
That said, you could for sure make it look nicer with the 4 colours they have. Using the blue and light grey for aa for example would work very well. and you could add more flourishes like a bit of a highlight on the edge of the disk, the little indention where the metal bit slides around in, the copy protection hole next to the label, etc.
Yeah, I am not sure how that works on Amigas exactly. I reckon they might have did a combo of that plus only 2 bitplanes.