USSR had several predominately Muslims countries; Azerbaijan, Kazakstan, Tajikistan, Turkmenistan, Kyrgyzstan, Uzbekistan and then the Muslim enclaves within Mother Russia herself; Abkhazia, Chechnya, Dagestan, and various native Muslim ethnicities scattered across the former union. We're not talking about migrants here, rather people who have lived under a Russian rule or Russian influence, many of whom were displaced under communism, moved around and relocated as Stalin saw fit.
No different than the British and French Empires which were over many Muslim lands, now they’re reaping the whirlwind.
i just did not realize that Russia/Putin permitted them to migrate right into Moscow itself