I can't read the article - do they explain why they think this is a "paradox"?
Reality: removing standardized tests means that universities have to put more weight on the rest of the college application, such as extracurricular activities which are often expensive and thus disadvantage poor kids.
Calling it a "paradox" is maybe a little hyperbolic, but basically it did the opposite of what they expected.
At least in public schools were you don't have an incentive to give everyone an A, maybe private schools are different.
I think the "paradox" is that you'd expect disadvantaged students to perform worse on standardized testing.