Methinks, you're confusing regular troops with volunteers (or mercenaries, as some would erroneously call them). No one here denies that there are a lot of Russian citizens fighting for Donbass in Ukraine, as no one denied Russian volunteers in the Spanish Civil War fighting against Franco. Obviously, some Russian citizens are even fighting for Kiev, but their numbers are miniscule at best...

If Russia had deployed regular troops IRL, Kievan junta would fall within 24 hours