Those are old Standards. There is a similar thing in Florida Board too.
NCEES uses a modern telemetry blah blah, statistics method.
But it is true that the general consensus among test takes is that it is generally 56/80 which is 70% , a safe figure.
Given how hard or easy a particular test was, the passing grade is curved to match the standards of previous tests. Basically people who passed it last time should be in a way similar to the person who passes this year.
Also, I dont think it just a flat number like 56/80; there might be some extra points when you do better than the average in a particular section and you lose some points when you score below the average, making the score hover around 56 but not exact 56.