While it is true that some "Eastern" Europeans can be racist, the "treatment" of black and asian students in Ukraine was heavily misrepresented in the media. The reason why they would be the last to board the trains was because there was a policy of first boarding only mothers with children (of whatever race). Then it was single females, and only then were foreign males allowed to board. I highlight the word "foreign", because Ukrainian men of military age were not allowed to board at all (with only a few exceptions). There might have been confusion since many of the students didn't speak neither Ukrainian nor Russian, and in Ukraine very few people speak foreign languages, certainly not the people who work in the trains. So not knowing the rules, some students tried to board the trains first, but they were of course forbidden from doing so, until all the mothers with children boarded first. Same thing when passing the border.