then again, how good a manager would she have made if she was bossing around colleagues to the point of them quitting?

Management is not just about qualification, it's also about the human aspect.

I have seen enough toxic femineity at work to say it is actually a thing, on par with toxic masculinity.

Or perhaps this guy perceived normal, appropriate management that he would have been perfectly fine with had it come from a man as “bossy” when it came from a woman.