As an involved, caring, loving, parent I don't get some of the "don't worry about it" comments. He's your son, you love him, you want the best for him. He may be wanting you to see it, and may want you to ask him, because he has had some thoughts or feelings he's trying to figure out but can't on his own. You are the parent, he's the child. Take your responsibility as a parent seriously and ask him in a loving, caring, non-threatening way, and find out what the quiz was really all about. Be sure to communicate your love and respect for him, whatever his answer is. It doesn't have to be wierd. "who cares if he's gay???" I do, if I'm the parent. I have to live with (or without) his decisions for the rest of my life. I care, a lot. I believe homosexuality is a choice. People say "They're born that way." I agree. I was born a killer. And a thief. And a liar. I choose to do or not do those actions every day. I've met several people I've wanted to kill. (when I was a heathen) Many times I wanted to steal something. I've told my share of lies in 43 years. Are some people more inclined to be homosexual? Absolutely. Are some people more prone to lie, or cheat, or kill? Absolutely. They were born that way. That's why we need Jesus Christ to fix our hearts, and minds, and souls, and wills.
PS Talk to a few of the many souls who have escaped the madness of homosexuality and listen to their stories. They'll blow you away. You talk about seeing the light. WOW. And then come back and see if you still say "there's nothing you can do", or "don't worry about it".