If there's one thing I've learned from attempting to replicate bugs, it's that if something affects even as much as one in four people, it'll look hunky dory to thrice as many people as it looks awful to.
I'm Canadian. White. Blonde. I'm often mistaken for a soldier. After possibly hundreds of trips in and out of the US spanning four decades, last month the guy at YVR asked me "what religion are you?" That was strange. I didn't have a ready answer and I'm someone who always has a ready answer for boarder guards. I actually said "Well, when my grandfather died we had a ceremony at a church. Is that enough?"
Have you ever been arrested? No. Have you ever been finger printed? Yes. Have you ever been to the middle east? Yes. Are you carrying food? No. What religion are you? .... wtf did that become a thing?
Interesting. I'm a white guy and I've gone through secondary screening (swabs, detailed questions, etc) probably half a dozen times over the past 2-3 years.
And I have a US passport!
My belief is that it's because I had gone through some pretty substantial weight loss in the past, and so my body skin/muscle/fat density is all screwy around the midsection, and thus it sets the machine off.
Most likely because all the aggressors in those incidents see is the traditional dastar.
Remember that one of the more prevalent slurs for men from Muslim cultures is "raghead." If you're already enough of a shit to think that's a legitimate way to treat people, you probably don't care one whit about the cultural specifics of the "rag" in question.