[silisili]

The other comments gave good answers. A lot of people think it means saying something horrible and racist or something, but not at all.

As one pointed out, there's a "well you said it was X, but person Y who got hired did that too. And they're a different race or gender or religion, so that leads me to believe discrimination."

There's also you trying to be helpful, saying something along the line of "well you hesitated a bit and sounded unsure in your answers", only to find out they have some disability that caused that and now have admitted you're discriminating based on it.

Maybe you'll say "well, if I had known, I wouldn't have noticed it or cared." And a lot of candidates would likely say as much up front. But they don't have to tell you about it at all. See how that creates a weird dynamic?

Is it common? Probably not. But it obviously happened or else such rules wouldn't exist. It's one of those things that the bad actors ruin it for everybody. Bigots are never going to admit their reasons - good people will. But bad people will always try to take advantage, regardless.