In case of Berkhamov-Tumenov, thing was that they are from the same Republic but of diffirent ethnicities. So things started to heat up (like, people of one ethnicity started to hate people of other ethnicity).
Also, about this whole thing Reznikov commented not so long ago -- you fight Russian/ex-USSR guy and then you might see him on the street/in gym and other places and feel yourself uncomfortable.
Plus, seems the whole mma scene if not that big in Russia and my feeling is that, for example among mma fighters from Dagestan 40 % (if not more) of them have brother/cousin/second cousin/father/uncle who is an mma fighter.
There was some examples of opposite -- Ismagulov offering to step up as a replacement and fight Tukhugov; Tukhugov and Lobov (but maybe Lobov doesn't count); Evloev said that he either moves down and fights Yan then fights Magomedsharipov; probably it's already a dozen of Dagestani fighters who said that they want to beat up Chimaev (also Reznikov remembered that Khamzat wrote some shit to him and would like to beat him for it, he also suspected that Khamzat is into recreational drugs (that's why he writes strange things in Russian) and Khabib's friend/pupil/mma fghter who is an ex-addict and now helps people recover wrote something like yes, Reznikov is right Khamzat writes/sounds like a person under influence of "salts" (I think it's called "alpha pvp" in English)) and I think everyone aside from Nurmagomedov-Makhachev said that they will agree to fight compatriot for a contender spot or belt.
Yeah, Amosov used the word "Rooskie" but some people used it to describe anyone with Russian citizenship.