I would say that it takes a lot of faith to make a statement such as Neandertals didn’t use projectile weapons this long after the fact, and with as little evidence as they actually have. Hundreds of thousands of years in existence, and not one of them ever picked up a rock and threw it at a hyena trying to eat its baby?
I don’t think so.
That's the evidence to date. I agree that they can't actually know.
As far as throwing things, Neanderthal shoulders were built a bit differently than those of other modern humans and could not throw with effective force. At the same time they were heavier, had larger muscles and could poke spears quite well.
Regarding throwing, there are wide variations among humans, and folks who spend their lives kicking soccer balls aren't at all good at throwing baseballs.