In my world if you make a serious allegation such as crowd racism you back it up with facts
I don't see any issue with making the serious allegation even if you don't have 'the facts'. What if a player was genuinely racially abused, but the stadium didn't have sophisticated audio technology to pick up the monkey noises? In this case should a player simply never make a claim?
I think if he did think he hear it, he was absolutely right to do what he did.
What makes me suspicious in this instance, and means I'm hesitant to assume he's telling the truth, is the fact he's made a claim before that wasn't backed up by evidence and the way he went down to Son's challenge shows he doesn't mind being deceitful for his own ends.