Such is termed a hypothesis -in the case of this subject article generally and in the case of a genetic cause specifically for the homosexual disorder - an unproven hypothesis
Well, sure. I thought that was the whole point of doing these studies on siblings and twins - to see if there is a genetic component to the chemical imbalance you described. It's unproven, certainly. But that's why they are doing research like this...
Do you have another hypothesis on what may cause the chemical imbalance side of the equation? I've seen lots of theories on the behavorial aspect, but very few on the chemical side of things.