I think being a woman means (and certainly is intended to mean) you're automatically part of an under-represented group - namely, that of women. There are (far) fewer women among Rust users than in the general population, which you could say is the (a?) definition of under-represented.
The percentages can add up to >100% because you can be part of multiple groups, e.g. a gay woman.
1. Yes, but if the "women" stats only come from a question about self-identifying as underrepresented, your "automatically" doesn't kick in. If women don't check that box, you don't know they're there.
2. I get that, I'm just surprised it's so pronounced. With most statistical distributions, when 0 (flavours of underrepresentation) covers 92% of responses, you'd expect 1 to cover a major chunk of the remainder, and that doesn't appear to be the case here.
The percentages can add up to >100% because you can be part of multiple groups, e.g. a gay woman.