>"...Afros, braids, twists and other hairstyles popular among black women."

They literally say so in the subtitle. The discrimination exists before people enter the airport, and it comes in the form of what hairstyle to choose. This is partly done on a cultural basis, and partly because of a different hair composition. But the important thing is, the machine does not differentiate on the basis of race, it's a machine that detects areas of suspect density that could presumably be hiding contraband. I am a white man with long dense hair, and my hair triggers the machine almost every time. Not because I look like a hippy, and Nixon is still running the show, but because I could hide things in my hair.

The fact that certain hairstyles are more popular within a racial group IS the discriminating factor, not the machine.