The involvement fair is a showcase of clubs on campus (environmental club, vegetarian club, republican/democrat club, etc.), in which the clubs recruit members and distribute information about their cause. The GLBT club is not allowed to recruit.
The club has to jump over a lot more hurdles than the other clubs in order to promote themselves or do something on campus.
There is a lot of diversity at my school, and a lot of gay and lesbian individuals. I have never been to a GLBT meeting, but I would imagine the discretion of the meeting is probably up to them, and they can talk about whatever they want to. After all, these are people in their 20s. Seeing as it is not a religious club, and only about 40% of the student body identifies as Catholic, I would seriously doubt they are discussing chastity issues.