There is no evidence Holgate did it on purpose. The FA handled this totally right (for once in their miserable lives). Punishing Holgate for reporting in good faith would set a terrible precedent. What would happen in Brewster gets abused again? He would be afraid to report it.
Firmino and Holgate both seem like they both want to move on. Bobby's statement was not angry at all and he was even sympathetic, having been racailly abused before himself. Holgate thought he heard something. He didn't. Move on.