ONLY and ALL are the two tests of a strict categorization method, but the use of either indicates an attempt to categorize. For instance, if ONLY the failing white kids are held back due to poor grades, but not ALL of the white kids are held back, while ALL of the black kids pass, regardless of performance, then obviously there is discrimination based on race. Sure, there may be a secondary method of discrimination, failing grades, in deciding what white kids to hold back, but that does not erase the race discrimination. The grades are obviously secondary since they were not applied to the black kids.
I am sure you will now claim that this actually happens or some bullshit.