He was using the huge social media following he has, purely due to his sporting career, to propagate beliefs at odds with his employer’s code of conduct.
I don’t even have a social media following to speak of (family and friends, that’s it), but you can bet your arse if I posted bigoted material, at odds with my employer’s code of conduct, and in violation of the social media policy I’ve received training on, they could sack me too. And whether I posted such material at work, while wearing uniform, yada yada...would have absolutely zero bearing.