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). Do not make the mistake of going all in and quitting your job until you start seeing consistent success with your gambling.
On top of this there are always good and bad sides of being professional gambler. Probably worst possible job this could be (from my perspective at least). But is this what someone wants. To be addicted to this, and to lose some not so good 9-5 or 8-4 day job, to be apart of your family. Dont think Im for this, and also think that many here are not for this as well.
If you are then you need to have control and self discipline, to choose online or offline gambling, many possibilities and many options on this.