unless there is a victory tax in his country which requires gamblers to pay PSJAK if they win,
I do not think there is a single country in the entire world where gambling winnings are tax-free;D. In gambling, it is either the house wins or the government. In my country Government takes (robs) 30% of gambling winnings. Even winnings from games like chess is also taxable
.
I am sure nobody gets paid in full in this sense.
In my country here in Nigeria, I dont think gambling winnings are taxed, well, I am not so very sure but personally, I've never received from a casino, less amount than I won on any excuse that the rest was used to settle my winning tax to the government, all the money I won from didffermt casinos have alway been complete when I receive them.
The Nigeria government don't actually pay attention to some of this things, but it's understandable because our government are one of the most corrupt in the world, they are always after the big companies that will be paying their tax in billions of naira, this money they do nothing with it, other than loot it and share it within themselves to keep for their generations to come.
Possibly the reason why they don't care about taxing gambling winnings as what they will be getting is very insignificant compared to what the companies and big businesses in the country are paying as tax.
There are exceptions and limits, and in general that isnt monitored much or government isnt very strict with income tax. Its very individual. They dont stress people a lot, but they can randomly chose anyone and force to pay income tax if you have sold your used mobile on Facebook marketplace for example 
