Why do people stereotype Womens Studies with lesbians?

I’m starting University in September and am thinking about taking women’s studies as an elective. I mentioned it to my friend as I was telling her the courses I was considering. She burst out laughing and said something like “you know that class is for lesbians right?”. It really bothered me that she would stereotype like that. I believe that women should have equal rights to men, and I guess you could call me a feminist. However, how does that associate with being a lesbian? I wanted to ask my friend, “oh so you think we should be oppressed and be subordinates to men?” Can you guys clarify why people harbour this stereotype?

Also, if anyone knows a little bit about this area of study, and opinions/info on it would be nice. P.S, I’m still taking the course because I’m not going to take something else just because the class is associated with lesbians. I’m no homophobe. (: