This was a college, not a church.
There is a fine line here. A Christian is free to witness to anyone receptive to what they have to say. However, they cannot engage in harrassing activities in order to witness. Others have just as much right not to be witnessed to as Christians do to witness.
If the purpose of a club is to promote, investigate, and examine a particular and specific area of study, as in a science club, then they have the right to expect that their members will abide by those activities that accomplish that. One joins a club to engage in activities with others of like mind. There are bylines that specify the purpose of the club and the expected behavior of club members. The right to expect that from all members is not unreasonable.
Likewise, sexual orientation should not be used as reason to dismiss someone from an organization. As hard as some find it to believe, there are homosexuals who identify as Christian, and practice their religion with every bit as much devotion and reverence as does a heterosexual Christian. Unless that homosexual is engaging, within the confines of that club, in a way that disrupts the activities of that club, then their sexual orientation is not a concern.