Your name is right in your profile, so pdx could have easily got your gender from it. Maybe pdx even opened your site, where you have a photo clearly showing your gender.
It's also possible that English is not pdx mother tongue, maybe pdx tongue is one of those where the male pronoun is used to refer to people when the sex is unknown. Also, while it's usage as this has been fading, "he" is defined as "Used to refer to a person or animal of unspecified sex" in many dictionaries, and someone could have been tough that in school (I have been).
It's also possible that English is not pdx mother tongue, maybe pdx tongue is one of those where the male pronoun is used to refer to people when the sex is unknown. Also, while it's usage as this has been fading, "he" is defined as "Used to refer to a person or animal of unspecified sex" in many dictionaries, and someone could have been tough that in school (I have been).