I'm just guessing and could be way off, but I think maybe it's a polite way of saying that you kicked something's ass ? Like if you did 5 loads of laundry all in one afternoon ( maybe you usually only do 2 ), you might tell someone, "I kicked ass !". Though again, I might be way off.
If the teacher is an older person, I can see being uninformed about 'pronouns'. I'm always reading about some new thing ( to me, anyway) that someone or some group of people want to be called. Non-gender specific is just weird to me. Of course, I was a teenager in the 80's, so none of that was around back then. At least, I had no knowledge of it. Back then, they weren't even that many people that would even feel comfortable with people knowing they were gay. It was the midwest, though, very conservative-- and I lived in a small town. I think that all makes a difference.