Sensownym wyjaśnieniem jest to:
Assuming they're using the 307.2MHz mode, then it's 2.5x clock difference. Further assuming it's only a linear scaling, then 1920*1080/2.5 = 1280x648. Simplest explanation then is that they didn't want to deal with any aspect ratio differences, hence 1152x648 (16:9).
Partacze z Retro niech się lepiej zajmo Labo a nie większymi grami