HeyScore is a ranking of an underlying number, which stems from the calculations performed by the algorithm. The ranking can change, even if the calculations yield the same number, if the basis for comparison changes.
The HeyScore shown when you view a stock’s page is relative to the stock’s home market. That’s the default HeyScore. In Screener results, the HeyScore is relative to the population of stocks that match the screener search parameters.
Suppose you sort students in a school class by height. A student’s position in the list depends on an underlying number, namely the height, and it is relative to the other students in the class (the population). The position might change without her height changing, if you form the list from the girls on her gym team rather than the class (different population). It might also change if you sort the list again one year later, after all the students grew taller. Now the underlying number changed.
HeyScore as a ranking behaves in the same manner.