Is it normal to be confused about people, by their looks?

I see so many people on campus that are queer. In my classroom you'll see the normal male and female. I did this: "Mr you didn't give me a paper" and they got mad. They said I'm a girl. Firstly, they were: sagging,had a shaved head, military jacket, some playboy shirt, and had on Jordans; the majority of guys would wear. She looked like a complete dude. I apologized but she threw a massive fit. I mean could you blame me for mistaking? She didn't have much breast (not to sound pervy). I'm just saying with everything, even her voice she seemed like a dude. Even with guys I see this. If they influence this, why do they have a problem? I mean isn't the mistake easy? I don't know everyone's names or know everyone so I can't just pick out whether they are something else with that look or not. I've seen girly males and tomboys before but not this much. (where I grew up this was rare, believe it or not). So...idk if it's mean to say that. But saying "it" "hey" really doesn't get much attention.