Why does is a first grade teacher questioning a student about their gender? Help me understand

So parent teacher conference was Nov 14th and My daughter's father went with my daughter. When he gets back with her my daughter is saying "I'm not a boy".." I don't look like a boy" I'm asking what happened, he then explains to me what happened when he went to see her science teacher. He told me he walked in to the class and she greeted him and then looked at my daughter and called her a boys names. Her father told me he was confused and made her aware that's not her name and she isn't a boy. The teacher then began to question my 6 year old on weather she was really a boy or not . And her dad explains again she's not a boy and asked the teacher " Does she really look like a boy to you?" And she said " Yes, she does look like a boy". The teacher then just continued on with the conference and my daughters father left. I was mad and have called for a meeting with this teacher. And I recently found out from another teacher at the school that she caught that same teacher in the hallway questioning a boy as in to why he's on the boys line. The teacher told me she had to step up for the little boy and tell the science teacher because he's a boy. I want to file a report with the superintendent but her father is telling me to wait til after the meeting. Please guys what are your opinions and what would you do in this situation?. I'll answer any questions. Thanks via /r/Parenting https://ift.tt/35bwugy