I'm not sure this study shows causation. The neural plasticity of the brain is well documented.... that is to say, if you use it in a particular way, then neurons grow in heavily used areas. If you look at a group of PET or MRI scans of a wide cross section of people, you can pick out who is depressed, who is a musician, etc... I'm not saying being gay is a choice, but I don't think this definitively shows the root cause.
There are also trends that can be picked out but it is not really proof. Anyways it does not really matter because even if some are by choice some are by biology some are by whatever, the end result is the same.
