This finding only makes sense. It is more likely that homosexuality is passed to children of homosexual couples because of the genetics. Think about it.
That would only apply if you eliminate situations where the couples adopted, or where one of the partners was formerly living as a hetero who had a child with a member of the opposite sex.
I will grant you that the article does not call out how these children entered the lives of these homos. Nevertheless, it's a sure thing that the two homos did not produce the children themselves.