It is practically the same. When it comes to limited entrance, you can't make it easier for a certain group without making it harder for the rest.
Say you have a minority that's 1% of the population, and unhindered it would also make up 1% of enrollments.
If you don't allow that minority to enroll, you're increasing the acceptance chance of a majority group member by just over 1%, while decreasing the acceptance chance of the minority member by 100%.
The correct way to describe this is then most definitely discrimination against the minority, and not affirmative action for the majority.
Essentially it was more difficult for Jews to get into university, neutral for Russians, easier for Tatars and some other minorities and extremely easy for what's called Northern Minorities (they had - and still have special quotas, no exams necessary)
Speaking as 1/4 Russian-Jewish, 1/4 Chuvash, 1/8 Latvian and 1/rest Russian.