No excuse to sell him in January and not have a suitable replacement in place given this will no doubt have been in the pipeline since last summer. As such, I'm surprised if he's just suddenly decided to go on strike - reckon a deal's done and he'll be gone in days.
Seemed fairly clear at the time that Holgate reacted to Firmino saying something along the lines of '(hijo de) puta'. So presumably he either recognised it as the insult it is, and it's been blown out of proportion, or misheard it as the N word.