Here are the things I noticed:
1) The study doesn't recognize bisexuality at all. This is a major flaw, since there are at least half a dozen people on my friends list who identify as bi and are married/in heterosexual long-term relationships. Behaviour is only one indication of sexual preference, and it is not necessarily the definitive one.
2) There's an underlying equivalence here between "social" and "environmental" that needs to be challenged. Environmental factors could include physical things like pollution that are not controllable on an individual level but could have an effect (to the best of my knowledge, that has not been ruled out as a scientific factor - someone correct me if I'm wrong, please.)
3) The conclusion - "Taken together, the study’s findings suggest that intact parents bearing multiple children and living in rural areas increase the probability of heterosexual pairings in their children." Really. I thought it showed a connection - but I didn't see any evidence of causality. It seems to me that the more insular and religious your family life, the less likely you are to be open about your sexuality if it doesn't match expected norms, leading to fewer homosexual marriages. Thus, social expectations increase repression rather than decreasing homosexuality.
All in all, I dislike the tone that parents can avoid that most horrible of outcomes, a homosexual child, if they just obey the teachings of their church regarding their own marriages. Of course, it's what I would expect from this source, but still - it grates.