I'm not sure this has been handled well by either side, TBH.
If Mackay really did speak to a steward, and the steward said it was a swear word but not a racist comment, then he'd have been better just keeping his mouth shut and passing on the steward's name to his bosses.
I'm also not really sure what benefit it was to hold up an anti-racism T-shirt to the County support, as it comes over (to me, at least) that you're tarring the whole support as being involved in any racist incident.
However, that's more of a heat-of-the-moment thing, and maybe emotions just got the better of him. Unlike Mackay, who given his history, should have kept well out of this.