The concept is designed to Drown out "Other-Noise"
When you hear a loud enough consistent White-noise.. It raises the sound-level threshold of your ear. So everything "Not" as loud as the white-noise you're using will in effect "feel muted/ or at least dimmer"..
Sudden noises, like car horns or a woman shrieking, would instantly distract you, because your brain thinks you might come under attack from that direction..
The consistent/ predictive nature of the white-noise itself will be filtered out by your auditory cortex as non-essential information.. and so you will not be distracted by white noise..