i doubt there is any country that is taxing bitcoin directly
But he won a lot of money. If he wants to buy something nice like a bike or a car (let alone a property), he will raise alarms and get investigated, so unless you want your bitcoins to buy beermoney stuff (small purchases) you'll end up forced to get it taxed.
he wasn't talking about that in his post, so i assumed that he does need to convert them for the time being, and in this case there is no need to declare anything
otherwise it go without saying that he need to declare is income in the event that he want to buy something big, especially in newwork when their rules ar every sever about bitcoin