I think there's a lot missing the point on this, some wilfully.
The offence itself doesn't sound like much, beyond a fourth official acting unprofessionally and clumsily trying to identify a member of the coaching staff, but for a lot of the players that have had to endure racism in their careers to date this was obviously the straw that broke the camel's back and, crucially for them, a subsequent opportunity to ACTUALLY say "no" to what they perceived to be racism rather than peddle a slogan round and do nothing real about it.
It is sad that only now are some black people feeling emboldened enough to stand up in the face of persecution and, in football as with anywhere else, we have to encourage them to do so, even if they're ultimately perceived to be "overreacting" to a gaffe arising from a language barrier, misunderstanding, etc.
People acting as if they think this will give rise to matches being abandoned every time the word "black" is mentioned need to give their heads a wobble. Players and teams should feel free to leave the pitch if they feel they've been racially abused, without fear of reprisal from their clubs, UEFA, FIFA, etc. Yes, when it becomes more common for them to do so, some instances will undoubtedly arise because something was misheard, mistranslated or misunderstood but that's fine, too. There is NO room for racism in the game (or anywhere) so it is infinitely better to "risk" very occasional abandonments or suspensions of games over misunderstandings than to let things continue as they are and give black players no protection whatsoever because we're concerned there might be said occasional abandonment.
Good on all players and staff involved for their solidarity in this. Hopefully this proves to be a big moment in the months and years to come.
