If it was 20 cm off it might just as well have been a few degrees off from being perpendicular to the road/parallel to the line that marks the finish.
The rules are the outcome of reluctant evolution since back in the 19th century, it's hardly surprising that the camera isn't necessarily considered the ultimate source of truth.
(history of techno and a road cycling race on the first lines of hn, today it's really looking as if tailored to mock my interests)