Im not a Medic, but thanks for my love at the police series, I know that you can know the sex of a person with his skull (but if you have the pelvis, you can know automatically the sex of a skeleton. I try to find the Pyro skeleton in the SFM model but I cant find him). I found this picture of the Pyro’s skull (with a alien infection).
I found this information
For disgrace, I think the team work designer of Valve know too that you can find the sex of a skull, so at first, they take a “bad radiography”. That means that you cant see the important parts that can help you to find the sex of the skull.
the only that you can find in the radiography are this general feature.
Is poor, but that can mean that the Pyro can be MALE, for disgrace the important parts are damaged.
Anyway I dont give up so the pyro have a cosmetic that show his skull
here you can get a better look
the red part are the most important, but the green can say if is a male or female and still loks like a male.
I am a completly amateur, but I think that the pyro is a Men. Anyway I hope that you like my theory XD