Don't know about that post, but in Russian Federation slavery really existsed in nearly all muslim Caucasus republics like Chechnya and Dagestan. Slaves was mosltly kidnapped or tricked by attractive contracts Russians, Ukrainians and Middle Asians from Tajikistan/Uzbekistan and Chineese and Vietnamese. Slave labour used on Caucasian factories. Looks like that slavery decreased, since Putin began to flood Caucasus with Russians tax money, so the need for slaves become obsolete. No need to have a real slaves to produce something when you have an unlimited incoming flow of money for free. However, all information about slavery on Caucasus are silenced now "to prevent etnic discord", against Caucasian tribes, of course, so it is hard to tell if it is really eliminated.

Of course, at the time, liberals, including Putin (f.e. see Kondopoga incident), care only about "Chechens oppressed by Russian nationalists" fight for their "unique culture specific", push tolerance, and never cared about slavery.

All in all, it is absolutely possible that Muslims could have black slaves right now.