He would of said Mbappe or Neymar because he knows who they are as does everyone. An assistant from the back room staff is different, he wouldnt of known them most likelyLooking at things it seems that the Romanian 4th official identified a player based on his skin colour rather than just pointing him out. The Romanian word for "black guy" sounds like "negro" - one player thought he heard negro and kicked off - Demba Ba has a better understanding of the language so recognised he meant the "black guy" and hadn't said "negro" but even so recognised it as lazy racism.
The idea that in a matter of seconds they could orchestrate things into a manoeuvre to stop someone being sent off is unlikely but the attitude of the official - i.e. he demonstrates that he holds one teams players to be of lesser value to the others is clear ( I bet he would have said Mbappe or Neymar had it been the reverse not "the black guy" ) which then gives them grounds to protest that the officiating team cannot be trusted in their eyes to play fair.
The big question now is what if the official gets found guilty do UEFA do about it? Their usual lame job?
What do they do about İstanbul Başakşehir ? Their usual instinct would be to come down on them like a ton of bricks but the eys of football will be on them.