~snip~
If anyone says they make a living by gambling, they are definitely lying.
Gambling means luck and it is not possible for a person to be lucky all the time.
Even if it is a game played with knowledge, luck is definitely required.
If you try to do this with sports betting, you still have to be lucky.
In short, I never believe that there is such a person. Sometimes people get lucky and win well, but sometimes they don't get lucky and lose a lot.
To be fair, the quote said "in gambling", not "by gambling", so although I absolutely agree with your point, that is, that most people will never be able to earn a living by gambling, because the odds are against them, the fact is that some people actually do earn a massive amount of money in gambling, that is, the owners of the casinos.
It's just simple math and probabilities, since the odds are against the gamblers, it means that the casinos always win in the long term, and that means that whoever owns the casinos are getting richer every day, and that's in gambling.