Got into an argument with someone over whether a character is "non-binary."

The character's name is Zoe Hange, from Attack On Titan.

According to this other guy, in the manga in Japanese, for some reason Zoe's sex is apparently never specified, thus this guy insists on referring to her with they/them crap--he also uses this as justification for that whole Yamato thing. "See? Other series do this. Get educated."

The anime, however, explicitly makes Zoe female, and voiced by women in both Japanese and English--were she non-binary, she likely would have been voiced in English by someone who claims to be such, like Michelle Rojas or Marianne Miller (now calling herself Marin Miller), but instead she is dubbed by Jessica Calvello, who is a normal woman.

Yet this guy only refers to Zoe Hange as "they" and crap like that.

I am not into Attack On Titan. Not my thing. But unlike One Piece's Yamato, I can't find word from the original creator on this, and I don't trust sites like TV Tropes to tell me the truth here. Thus, I turn to you.

If the mods feel the need to remove this, I will understand. I'm just not sure who else I could ask this.