Not necessarily wrong. Let's say it's inverted with respect to what you would normally expect. Since PUT writes pixels with XOR, it doesn't make a difference after the two PUT are executed. But since the graphic mode doesn't have double buffering, the screen could refresh while the PUT are executing. If the sprite is erased and then the next sprite is drawn, it might happen that you see no sprite or a partial sprite for a split second. If the next sprite is drawn first, and then the previous sprite is erased, you might see something like two slightly different sprites at the same time, and this gives a better (still ugly but better) movement effect in my opinion. That's why I inverted those lines.