Control is a rather mythical thing that everyone aspires to, which I think is right.
But to achieve control, or rather, to realize that control has been achieved, you need to put yourself in a situation in which you usually lose control, and this time hold it.
In my opinion, control is an opportunity to stop gambling painlessly following your strategy during an irresistible desire to continue.
Therefore, it is so important to have a well-developed plan, following which you will not lose control.
Controlling how you gambling does not mean that the person or gambler should completely stop it or else its a personal choice. If could be a strategy that à person develop that keeps him or her going in gambling.
Moreover some gamblers have control at the beginning of their gambling experience, some happens to develop theirs after experiencing series of addiction and recovering from it.
The control that they're referring to is about time and money that you spent on gambling. You should learn how to self-exclusion 'cause when you feel you're playing too much and spent already a lot of money, you can ask to be self-excluded on the game.
Learn how to time-out also, it can be used if you want to keep playing, but handle it by withdrawing yourself from it for a short time. These two things are very important and it's part of the control.