That Joan comment annoyed me too, though I didn't say anything at the time. Not your fault, but just let a woman do something remarkable, something almost miraculous, and sure enough, some man 500 years later is going to claim that she must have actually been male, genetically speaking.

She is a woman, regardless of whether she has a Y chromosome. It is SRY gene that matters genetically. So we can use that observation to free us up to call evidence evidence without committing crimes against womankind.

If I my (most decidedly female) lecturer is to be believed the speculation was based primarily on personal reports from her closest friends. It included things like menstrual patterns (and the lack thereof) and personal habits. I didn't look into the details to see whether or not the this was an allusion to the typically far shorter vagina becoming relevant. I'm also not sure if the line of reasoning was prompted by some historian trying to work out what on earth was going on while researching her personal life or just biologists liking to feel like their knowledge is relevant to impressive people and events.

If she hadn't done famous things then we probably wouldn't have any records whatsoever to go on and nor would anyone care to look.