I think it would be more likely that the staircase fit better going one direction than the other. Eg taking the most used path to the staircase and going straight onto the stairs vs having to do a 90 degree turn before you can step on the stairs.
It seems unlikely that random chance would lead to a 70/30 ratio for "best fit" either, so that just seems to be moving the phenomenon that needs explanation to layouts around stairwells, which certainly weren't standardised in the medieval era.
The ratio of staircases in Norman castles was more like 20:1 which is a ratio even more in need of a non-chance explanation; the greater numbers of anticlockwise staircases came later, when coincidentally or otherwise individual towers were less important to the overall defensive scheme
