Actually it was common sense to think Yamato was a woman just back then with the intro of her character. A lot of people did not understand that she wanted to be like Oden not in the sense of his gender.
Btw this emunopla guy,
in my opinion, is wrong when he talks about "there is no love for the same gender". It's just religion bullshit. I'm an heterosexual man btw but for me two men and two women can still love each other.