Natural selection means that a trait like male homosexuality, if it had a genetic component, couldn't have persisted over evolutionary time if the individuals that carry the genes associated with that trait are not reproducing.
In my observation of two contrasting cultures that I grew up in, it could be better explained by sociology than genetics.
We have genetic diseases that kill people before they reach adulthood. We have gay people who get married, make kids, and feel zero sexual attraction to their spouse.
Evolution is a complex process. It's not a mere "more offspring = everyone else disappears" deal.
It can be evolutionary advantageous for some of your kids to come first, even if it means others come last, rather than all your kids coming second.
A "male gay gene" could evolutionary surivive if it leads to boy crazy girls. Vice versa for a "lesbian gene".
In fact the study did find that partly different genetics were correlated for lesbians and for gays.
Not really, if we go back to time people were prosecuted for being homosexual. They used to have a wife and kid but still practised homosexuality in private or killed their desires and gave it up at great pain and sufferings.
It will take time for natrual selection to remove Homosexual genes (if we believe they exit) if they've full freedom and aren't forced to have kids.