These studies on sexuality involving identical twins are always suspect. Having an identical twin is an extremely rare experience, definitely very different from the mainstream both genetically and socially, and yet somehow these groups are posited to be representative of all humanity?
It's also interesting that the study involved 37 sets of twins where one was hetero and the other gay (how did they even find that many???), and 10 sets where both were gay (which is stated to be the more common situation - so why didn't they find more?). But apparently their study did not involve any hetero-hetero sets of twins, which you'd expect to be the most common occurrence. Why not? Have they never heard of a control group?
It isn't surprising that every single expert interviewed who was not directly involved in the study met these results with skepticism.