My guess would be that with the huge amount of American males (it is a big country after all) people just assume. And women are known to care about animals more, whether that is true or not.
I’ve been called a guy before and my name doesn’t exactly strike people as male. I am female. I’ve been on the internet long enough not to care.
I’m very interested in understanding. But I don’t want to always be the smartest person in the room. I’m already the smartest in most situations I’m in IRL. If it was always like that, I’d definitely go crazy.