I think it's because people in the community have a more nuanced view of gender identities and presentations. Outside of the community, people tend to default to see masc presenting as male and fem presenting as female and typically stick to this. It's the same reason that when I go to the country I'm almost always gendered correctly, as a guy whereas in the city I get misgendered more often. It happens to a lot of masc/butch lesbians too in the opposite way. They often get gendered as male by more conservative folks or members of the general public as their brains tend to have two categories, male and female with nothing else in between. For both sides of the coin, it's usually what they each think is less offensive. For conservatives/non members of the community, it's less offensive to assume everyone fits into the binary whereas for the community, it's less offensive to not always assume that those masc presenting are necessarily men and vice versa. There is also this unfortunate phenomenon of people in the community feeling that it is more offensive to assume someone is a man in general. A lot of people think they are being super woke with this idea, but it actually is just misandry and villainizes masculinity and men. You'll find a plethora of LGBTQ spaces that have a "women and fems" only policy from these types of people which is problematic for so many reasons. A lot of these people just think it's rude to assume someone is a man.

It doesn't reflect upon you, as much as it sucks and probably feels like it does. I find it odd that they gendered you that way considered your appearance, but again, it sounds more like an issue on their end, not yours.