That's why it says "no single genetic cause" and not "no genetic cause".
But yes, that's not necessarily malice or incompetence on the part of the title's author.
If it's not malice, then it's linguistic incompetence.
Language can be used in too many ways and not all correct ways to use it are also easily understood. Often enough that doesn’t matter because of context but here context leads actually to people coming to the wrong conclusion because the well known conflict is between some (any) kind of genetic origin of homosexuality and environmental factors being responsible.