Isn’t that the whole point?
You can be an anti vaxxer, that’s your prerogative, but when attending the event requires vaccination, you can either a) be a Sandgren and stay away or b) be a Tsitsipas, suck it up and get vaxxed in order to compete. Both are completely fine from a personal moral and legal POV.
Novaxx chose option C aka using his status and concoct some bs excuses in order to circumvent the rules that everyone else must abide by. That shit may fly in Serbia but fortunately Aussie people care enough to raise a stink about it and now he has to face the consequences of his choice, just like us peasants.