How on Earth do you know this?
Oh come on. They get shafted over by two decisions against them, their fans start throwing things onto the pitch and even injuring their own steward. They need an excuse not to have him as a referee again and something to take away the focus on their own fans. Also for the past year or so they have been outed as supporting a player who having said racist remarks and need to give everyone the "We are not racist" look.
Oh and on top of that the referee is recorded, so yeah a well known referee is just going to go ahead and be recorded saying racist things twice in one match and only towards one team and not the other.
This