No deposit Casino
means you can receive a bonus without any counterclaims on you. As soon as you play with your bonus once, it's done. There is no requirement for you to wager the bonus a certain number of times before a withdrawal can be made.
Instead, you receive the bonus, play with the bonus and if you win, you can choose whether you want to play further or withdraw the money.
In other words, you never have to use your own money when playing casino without wagering requirements and thus you do not risk a loss. If you do not then of your own free will choose to continue playing after you have used your casino bonus without wagering requirements.