Here is something I think we all forget now that we are all older and have experienced life. About 25 years ago when I was a teenager getting ready to start that college journey this would have freaked me out. Even today in 2016 most kids have not been exposed to the gay culture except for what they see on TV. Now they may have been around gay people but never know it. A lot of teenagers aren't sure if they are which creates a lot of stressful situations for them or they know and not sure how to interact in the world as an out gay person. Kids don't have the life experience USUALLY to function in these situations. But as they get older and experience the world this attitude changes - well it changed with me. I have no problem around LGTBQ people and that is finally me getting some maturity although I act like an idiot in many other areas of my life.
I don't think we need to cast judgement on the OP son for reacting this way. At some point he will learn and mature to be able to function in the real world that we all do.......or he won't and he will rightly be projected as a close minded racist / bigot / whatever. But if that's the case then it's a taught behavior and that falls on the parents. I like to believe he will learn to be more open minded.