It's not difficult.
I'm a senior member of management, a science dean and a professor of biochemistry at one of the most prestigious UK universities. In my time in academia, I've lectured students in chemistry, biology and biochemistry. Part of my training some years ago involved a stint as an Admissions Tutor at Central England university where I was responsible for interviewing sixth-form and FE college applicants who wished to study chemistry at degree level.
The interview technique concentrated mainly upon a very low-key, friendly and informal discussion with the applicant about their interests outside chemistry and university over and above what had been entered on the UCCA form.
These Russian scientists look for logical reasoning traits in young people which is invariably based upon their own methods of thinking. They discuss with them their hobbies and interests outside their favourite academic subjects and look for commitment and enthusiasm in these hobbies and interests. Time devoted to these interests is also important in the assessement. For example, if a student is a member of an amateur theatre group and spends a couple of weeks at a stretch at evening performances, this might demonstrate a person more inclined to the humanities than the sciences. Such a student might also find it difficult to find the time to study outside the confines of the university.