Re: Is it discrimination
A have a few female coworkers at the moment and I appreciate them very much. Smart, hard working, dependable, well mannered, and I really mean all those things (which also generally apply to my male colleagues as well, it's a really nice team). I absolutely wouldn't turn anyone's job application down based on gender, race etc, but that is one thing.
A completely different thing is: you have an offer for which you will pay to be displayed to people on Facebook; you can't have it displayed to everyone as it's prohibitively expensive; therefore you pick parameters of a population that's most likely to respond positively so that you can get the best response for your money; if the job is in the US, you probably don't need to show that message to people in Germany; if 16/17 professionals in that branch are male, you target men with that paid ad. Because if you, say, pay $100 to have the job offer shown to 10000 random people, the expected number of truckers that you reached is 100. If you pay the same $100 to show the offer to 10000 random men, you've most likely reached somewhere around 200 truckers (supposedly, there are around 3.5M truckers in the US). The yield doubles.
That's unless you have reliable access to much more private information about everyone, such as previous job experience (in which case, of course, you pick those who have worked in the field), and that still doesn't mean that you turn down women who apply for the job.