Interesting quote.
Statistically, if you add up all these 'historically marginalized groups', it seems like you end up with the overwhelming majority of the population.
Women are a bit over half. Then add on all non-straight people, all non-white people, all people with some serious health (mental or otherwise) diagnosis. Globally this covers like 95% of the human population. Even in America these 'historically marginalized groups' are like 75-85% of the population.
I suspect the complainant is casting a wide net when they try to define who counts as 'historically marginalized groups', to the point where this could happen by random chance. Though it's hard to know without knowing the full profiles of everyone at the company.
Also we can note that these 'historically marginalized groups' tend to concentrate in certain types of jobs; if a company were to downsize their HR department for example, they'd be firing nearly all women even without targeting women, just as if they were to downsize programming they'd be firing nearly all men.