Gonna go out on a limb here and guess that homosexuality is a complex phenomenon with complex causation.

SSM removes a taboo, essentially removing a barrier to same-sex experimentation, especially for those who are not “hard coded” in their sexual orientation or who by nature are explorers or boundary pushers. First-time sexual experiences have a strong imprinting effect on the sexual makeup of a person.

Also, it may be that pyschologists were wrong in dropping long-held conventional beliefs about what “makes” a homosexual, as in failure of a boy to grow out of the “girls are yucky” stage, or failure to properly bond with a father (if there was one in the home.) The switch to a “born that way” model by the APA was not supported by most of its members at the time, it was a political decision by those who headed the organization.

The link between sexual trauma (molestation, either heterosexual or homosexual) during childhood and homosexuality has long been observed and noted, but is not spoken of due to political correctness. Take an informal poll among your gay friends and ask them their age of first sexual encounter. You’ll be surprised at the number who were sexually molested at a young age.

So, your above referenced study does not surprise me. Children raised by gay parents would likely not be raised to have a taboo against homosexuality.