Chuncky pixels refers to the "1 byte = 1 pixel" in this case, both the Atari and the Amiga had bitplanes, where the separate planes where interleaved into the bytes, this was a product of hardware limitations at times, for example using bitplanes you could do foreground graphics without the need to redraw the background graphics when the foreground moved, something that was valuable since the slow hardware (CPU and memory) could hardly keep up with the racing raster beam otherwise.