Emily's Cat
Rarely prone to hissy-fits
"The claim sex is bimodal suggests we can make a measurement on an individual and use that to plot them along a distribution."
To nit-pick, a categorical variable can have a mode since the mode is a frequency count. However, the accompanying graphs showing overlapping continuous distributions make it clear they are not thinking about sex as a categorical variable.
Trying to remember my stats work... I'm inclined to say that categorical variables can have modes as a result of frequency counts among several categorical variables... but they cannot have a bimodal distribution. to have a bimodal distribution, the data being evaluated has to at minimum be ordinal.
You can make a picture based on non-ordinal categorical data so that it looks like it's bimodal, but that's an artifact of an arbitrary arrangement. And because there's no inherent order to the data, any perceived bimodality is at best a false impression and at worst the result of intentional misinformation.
Sex isn't ordinal, thus it can't be a bimodal distribution. Personally, I think the insistence that it's bimodal is intentional misinformation.