Well, it is right that the player should have any complaints taken seriously. And it goes without saying that if it did happen, ban the people involved and involve them in a community scheme to help them see people as people regardless of colour.
But if after an investigation involving the police, nothing can be found from the 1000s of cameras, staff, other players, other fans etc. Then you have to look at other reasoning.....
Player misheard something. Fair enough. Genuine mistake, but that player will be found out if he keeps crying wolf.
Or it was a con job, a deflection, an attempt to break up play.
Players dive, feign injury, hound the ref to influence decisions, handball goals, try to get others booked and sent off, make cynical fouls to break up play, claim for corners and throw-ins even when they know it touched them last. They spend 90 minutes trying to cheat and con the ref.
This could just be the next level. Playing the race card.
The competitive football pitch is not an arena upon which to place a moral high ground and its certainly not the last bastion of honour.