Am I remembering something wrong? I could have sworn he knew she was a women when he first saw her in the novel...
Edit: A little different from what I remember but yeah.
From the novel:
What, a man? I’m not int……!”
While I was staring at the [Crimson Eagle], we accidentally made eye contact.
That sharp piercing gaze reminded me of raptors.
When I made eye contact, I was convinced. That that person is a woman.