The general idea here is that when you are part of a majority, it's alarmingly easy to accidentally set up your community in such a way that makes those from a minority feel less welcome. It's a potential unknown-unknown. I assume the Rust community is trying to find out if this is the case.

Put another way, your skin color, sexual orientation, gender, etc. likely will not change your contribution. But if it turns out that people of a particular skin color, sexual orientation, gender, etc. are somehow disincentivized from contributing, that's a problem.