The "A personal story of Tanya Khovanova" section at the start of the article itself describes the method more explicity: "One of the methods they used for doing this was to give the unwanted students a different set of problems on their oral exam."
The introduction adds that the Jewish (or otherwise "undesirable") students "were given these problems one after another until they failed one of them, at which point they were given a failing mark."
The introduction adds that the Jewish (or otherwise "undesirable") students "were given these problems one after another until they failed one of them, at which point they were given a failing mark."