I don't think women are witholding sex in that way at all. When a woman decides to have sex is up to her. If a guy is bothered that he can't have sex unless he gets to know her first and decides to be in a relationship, then he can move along. I have only recently decided that from now on I'd prefer to get to know someone and develop feelings for them before I have sex with them. I'm fed up with meaningless sex, or sex that only means something to me. I suspect that means that I'd have be in a relationship with them. If a guy really liked a girl, he'd respect her needs/wishes and wait. He'd want the relationship too. There shouldn't be any problem with that.
I was just warning this guy that if we met, we wouldn't be having sex, and I was making sure that it was clear that my aim was to be in a long-term relationship. A lot of guys know they don't want one, but you don't find that out until you've been on a few dates and decided you like him! I'm not trying to trap or trick anyone. I'm just being honest from the get-go so I can spend my time wisely.
He still asked me to Whatsapp him!