What is misgendering?

When I was 15 and used to play Judo, I didn't used to carry a watch while going to practice, mobiles were not there in my country at that time. While taking a break from practice, I went to Table Tennis area, and started watching the game. I was behind a guy who was playing quite good. I needed to know the time, so I waited till one of them missed the ball. I asked the guy, "What's time bro". As he turned back to tell me the time, she turned out to be a girl with boy cut hair style and wearing boy's clothes. I just slipped from there silently.

I guess I did the mis-gendering.