Statement is true. There are people who live out of this, but for what cost.
Making money as a professional gambler is not easy. Some rules need to be followed, like need to be better than your opponents, minimise big losses and maximise gains. Also You need a good deal of practice in order to build the right level of skill needed to start off a gambling career (this may be tricky cuz it depends from type of game you want to be professional).
It is worth noting that you simply can't become professional in many games, such as dice, slots, roulette, minesweeper, plinko, and also maybe some others. Some people believe that sports betting is skill based, and almost everyone agrees that poker is more about skills than about luck, and yet it is not clear what exactly you should learn to play poker better.
I write this because I know that there are people who think that even for dice and slots you need a lot of practice to be a professional in these games, while, in fact, even in poker most can achieve little with practice.